Add controller input and a laser-pointer-driven menu quad

- xr_input.c/h: an OpenXR action set (aim pose, trigger/select click, a
  menu-toggle button) plus ray/quad hit-testing, and a visible
  laser-pointer line drawn from the controller toward the hit point.
- xr_menu.c/h + MenuOverlay.java: a second composition-layer quad,
  toggled by a controller button, showing an off-screen, never-attached
  Android View tree (one "Keyboard" button so far) driven by synthetic
  touch events computed from the laser ray's hit UV.
- Migrate gl4es from a prebuilt binary baked into the Docker build-image
  to a vendored source snapshot (android/gl4es-src/) compiled from
  source at APK build time via CMake add_subdirectory(), patched through
  a new android/gl4es-patches/ (mirrors the existing engine-patches/
  pattern). This was needed to track down and fix a bug hit while
  building the menu: gl4es's fixed-pipeline emulation (fpe.c) was
  unconditionally substituting its own shader onto the menu's draw call
  (fpe_ReleventState() always sets alphafunc to a nonzero sentinel, so
  its fpe_IsEmpty() check could never see the state as empty), making
  the menu quad show the game's own rendering instead of its own
  content. Fixed by routing the menu's blit through a real
  glBlitFramebuffer() call instead of a shader-based draw, which gl4es's
  fpe.c has nothing to intercept - documented in README.md's new
  "Debugging notes" section.
- Renumber android/engine-patches/ to close the gap left by removing an
  unrelated diagnostic-only patch, and strip investigation-journal
  comments and dead diagnostic code (temporary tracing, env-var probes)
  left over from finding the bug above.
- Restructure README.md into numbered sections, document every
  engine/gl4es patch, add Android Studio dev/testing-cycle instructions,
  and generalize Quest-specific wording to any OpenXR headset. Update
  NOTICE.txt to match (gl4es is now vendored/patched source, not a
  prebuilt binary; add the OpenXR-SDK loader).

android/app/build.gradle

@@ -4,18 +4,25 @@ apply plugin: 'com.android.application'
 // build-apk.sh, or standalone with --host-paths to prep for a native
 // build in Android Studio - see README) since they're only known at
 // prep/build time, not something a checked-in build.gradle can hardcode.
-// engineDir is the scratch, patched copy of engine/; prebuiltDir is the
-// Android SDL2/SDL2_mixer/fluidsynth-lite/gl4es prebuilts - both point
-// into this container's own paths for build-apk.sh's own gradlew call,
-// or host-resolvable paths (plus a host-side export of prebuiltDir, since
-// /opt/prebuilt/android only exists in the image) when prepared with
-// --host-paths for Android Studio.
+// engineDir is the scratch, patched copy of engine/; gl4esDir is the
+// scratch, patched copy of android/gl4es-src/ (built from source as a
+// CMake subdirectory of engine/'s own native build below, not prebuilt);
+// prebuiltDir is the Android SDL2/SDL2_mixer/fluidsynth-lite/openxr
+// prebuilts - all point into this container's own paths for
+// build-apk.sh's own gradlew call, or host-resolvable paths (plus a
+// host-side export of prebuiltDir, since /opt/prebuilt/android only
+// exists in the image) when prepared with --host-paths for Android
+// Studio.
 def engineProps = new Properties()
 file("${projectDir}/../engine.properties").withInputStream { engineProps.load(it) }
 def engineDir = engineProps.getProperty('engineDir')
 if (engineDir == null) {
     throw new GradleException("android/engine.properties is missing 'engineDir' - run via build-apk.sh or prepare-android-project.sh, not gradlew directly")
 }
+def gl4esDir = engineProps.getProperty('gl4esDir')
+if (gl4esDir == null) {
+    throw new GradleException("android/engine.properties is missing 'gl4esDir' - run via build-apk.sh or prepare-android-project.sh, not gradlew directly")
+}
 def prebuiltDir = engineProps.getProperty('prebuiltDir')
 if (prebuiltDir == null) {
     throw new GradleException("android/engine.properties is missing 'prebuiltDir' - run via build-apk.sh or prepare-android-project.sh, not gradlew directly")
@@ -27,14 +34,29 @@ if (prebuiltDir == null) {
 def questshockVersionName = project.hasProperty('questshockVersionName') ? project.property('questshockVersionName') : '0.0.0-dev'
 def questshockVersionCode = project.hasProperty('questshockVersionCode') ? project.property('questshockVersionCode').toInteger() : 1
 
-// Auto-refreshes the staged, patched engine/ copy and prebuilt libraries
-// (see build-image/prepare-android-project.sh --host-paths, and the
-// engineDir/prebuiltDir properties read above) so a plain Android Studio
-// build/run can never silently compile against a stale scratch copy after
-// engine/ or android/engine-patches/ change - previously a manual, easy to
-// forget re-run. inputs/outputs are declared so Gradle skips the (Docker-
-// invoking, not free) step entirely when nothing relevant actually changed,
-// keeping pure-Java edit/run cycles fast.
+// Auto-refreshes the staged, patched engine/ and gl4es-src/ copies and
+// prebuilt libraries (see build-image/prepare-android-project.sh
+// --host-paths, and the engineDir/gl4esDir/prebuiltDir properties read
+// above) so a plain Android Studio build/run can never silently compile
+// against a stale scratch copy after engine/, android/engine-patches/,
+// android/gl4es-src/, or android/gl4es-patches/ change - previously a
+// manual, easy to forget re-run. inputs/outputs are declared so Gradle
+// skips the (Docker-invoking, not free) step entirely when nothing
+// relevant actually changed, keeping pure-Java edit/run cycles fast.
+//
+// This step only re-stages whatever is already baked into the build-image
+// (it re-runs prepare-android-project.sh inside the existing image, which
+// is fast - no compilation happens here) - engine/ and gl4es-src/ are both
+// then compiled from these scratch copies by the externalNativeBuild CMake
+// configure below (see android/engine-patches/02-android-opengl-es.patch's
+// add_subdirectory of gl4esDir), so Gradle's own incremental CMake/Ninja
+// build only recompiles what actually changed, same as any other native
+// source edit. This task does NOT rebuild the image itself: if you changed
+// build-image/Dockerfile (a real toolchain/dependency change, not
+// engine-patches/ or gl4es-patches/, which this task re-stages on its own),
+// you still need to run ./build-image.sh yourself first (a slow, deliberate
+// step - see the memory on build-image versioning) so the image actually
+// contains your changes before this task re-stages them.
 def repoRoot = file("${projectDir}/../..")
 def stageEngineTask = tasks.register("stageEngine", Exec) {
     group = "build setup"
@@ -55,8 +77,11 @@ def stageEngineTask = tasks.register("stageEngine", Exec) {
 
     inputs.dir("${repoRoot}/engine")
     inputs.dir("${projectDir}/../engine-patches")
+    inputs.dir("${projectDir}/../gl4es-src")
+    inputs.dir("${projectDir}/../gl4es-patches")
     inputs.file("${repoRoot}/build-image/Dockerfile")
     outputs.dir("${repoRoot}/build/android-engine")
+    outputs.dir("${repoRoot}/build/android-gl4es")
     outputs.dir("${repoRoot}/build/android-prebuilt")
     outputs.file("${projectDir}/../engine.properties")
 }
@@ -102,8 +127,12 @@ android {
                 // SDL2_mixer and FluidSynth via the same build_ext/ BUNDLED
                 // convention the desktop build already uses (populated in the
                 // scratch engine copy by prepare-android-project.sh from
-                // prebuiltDir). ANDROID_PREBUILT_DIR is also read directly by
-                // android/engine-patches/02-android-opengl-es.patch, for gl4es.
+                // prebuiltDir). ANDROID_GL4ES_DIR is read by
+                // android/engine-patches/02-android-opengl-es.patch, which
+                // add_subdirectory()'s it to compile gl4es from source as
+                // part of this same CMake configure, instead of linking a
+                // prebuilt .so - so gl4es-patches/ changes just need a normal
+                // rebuild here, not a build-image rebuild.
                 // The CMAKE_FIND_ROOT_PATH* overrides below are needed
                 // because the NDK toolchain file restricts find_package/
                 // find_path/find_library to its own sysroot by default,
@@ -113,17 +142,28 @@ android {
                 // -Wl,-z,max-page-size=16384: NDK 26 doesn't 16 KB-align ELF
                 // LOAD segments by default (only automatic in NDK 28+) - see
                 // build-image/Dockerfile's ANDROID_16KB_LDFLAGS, which does
-                // the same for the prebuilt SDL2/SDL2_mixer/fluidsynth-lite/
-                // gl4es .so's this links against.
+                // the same for the prebuilt SDL2/SDL2_mixer/fluidsynth-lite
+                // .so's this links against (gl4es is compiled here with the
+                // same flag passed straight through, see its add_subdirectory
+                // above).
                 // ANDROID_EXTRA_SOURCES is a semicolon-separated CMake list,
                 // not shell-split - AGP passes each "arguments" string
                 // straight through as one argv element to cmake, so the
                 // ';' below survives intact. ANDROID_EXTRA_INCLUDE_DIRS lets
                 // engine/'s own OpenGL.cc find "xr_session.h" (see
-                // android/engine-patches/11-android-openxr-cmake.patch,
+                // android/engine-patches/10-android-openxr-cmake.patch,
                 // which adds it to include_directories()).
+                // USE_ANDROID_LOG/STATICLIB used to be passed to gl4es's own,
+                // separate cmake invocation in build-image/Dockerfile - now
+                // that it's add_subdirectory()'d into this same configure,
+                // they need to be set here instead, or gl4es silently falls
+                // back to stdio logging, which never reaches logcat. ANDROID
+                // itself doesn't need setting here - the NDK toolchain file
+                // already defines it before any CMakeLists.txt runs.
                 arguments "-DENABLE_SDL2=ON", "-DENABLE_SOUND=BUNDLED", "-DENABLE_FLUIDSYNTH=BUNDLED", \
                     "-DANDROID_PREBUILT_DIR=${prebuiltDir}", \
+                    "-DANDROID_GL4ES_DIR=${gl4esDir}", \
+                    "-DUSE_ANDROID_LOG=ON", "-DSTATICLIB=OFF", \
                     "-DANDROID_EXTRA_INCLUDE_DIRS=${projectDir}/src/main/cpp", \
                     "-DCMAKE_PREFIX_PATH=${prebuiltDir}/sdl2", \
                     "-DCMAKE_FIND_ROOT_PATH=${prebuiltDir}/sdl2", \
@@ -131,7 +171,7 @@ android {
                     "-DCMAKE_FIND_ROOT_PATH_MODE_LIBRARY=BOTH", \
                     "-DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=BOTH", \
                     "-DCMAKE_SHARED_LINKER_FLAGS=-Wl,-z,max-page-size=16384", \
-                    "-DANDROID_EXTRA_SOURCES=${projectDir}/src/main/cpp/questshock_native.c;${projectDir}/src/main/cpp/xr_session.c"
+                    "-DANDROID_EXTRA_SOURCES=${projectDir}/src/main/cpp/questshock_native.c;${projectDir}/src/main/cpp/xr_session.c;${projectDir}/src/main/cpp/xr_input.c;${projectDir}/src/main/cpp/xr_menu.c"
                 abiFilters 'arm64-v8a'
             }
         }