Add a standalone Android app with the same daily reading and config page

android/ links engine/src/ and interpreter/src/ via JNI/CMake (real
astronomy.c, not the watch's size-constrained substitute), rendering
through Jetpack Compose with a burger-menu config page mirroring
WatchConfig and a WorkManager-driven daily notification. Independent
of the watch app - neither requires the other.

build-image now bundles the Android SDK/NDK alongside the Pebble SDK
(VERSION bumped to 2), and .gitea/workflows/build.yml/Makefile/
run-image.sh build and publish the APK the same way as the CLI
tarball and .pbw.

README.md

@@ -59,11 +59,19 @@ watch/                            The actual Pebble watchapp - links engine/src/
                                   notification, and config page. Built separately
                                   from the rest of this repo (`make watchapp`,
                                   below) - requires the Pebble SDK.
+android/                          A standalone Android app (independent of the
+                                  watch app - neither requires the other) with the
+                                  same daily reading + config page, Jetpack Compose
+                                  UI, links engine/src/ and interpreter/src/ via
+                                  JNI/CMake (see CLAUDE.md's "Android app
+                                  packaging"). Built separately (`make android`,
+                                  below) - requires the Android SDK/NDK.
 docs/                            Architecture/dataflow diagrams, input/output format reference.
 build-image/                     Dockerfile for the reproducible build environment
-                                  (C toolchain + Pebble SDK) used by CI and by the
-                                  build-image.sh/run-image.sh/upload-image.sh scripts
-                                  at the repo root (see "Building" below).
+                                  (C toolchain + Pebble SDK + Android SDK/NDK) used
+                                  by CI and by the build-image.sh/run-image.sh/
+                                  upload-image.sh scripts at the repo root (see
+                                  "Building" below).
 Makefile                         Single root Makefile, builds both engine/ and
                                   interpreter/, and packages a release (`make package`).
 ```
@@ -98,6 +106,16 @@ make watchapp # -> dist/deck-in-a-dash-<version>.pbw, same version
               #    resolution as `make package`
 ```
 
+**Building the Android app** (`android/`, a standalone app independent
+of the watch app) needs the separate Android SDK/NDK
+(`ANDROID_HOME`/`ANDROID_NDK_HOME` set - see `android/README.md`), so
+it's likewise a separate target:
+
+```bash
+make android  # -> dist/deck-in-a-dash-<version>.apk, same version
+              #    resolution as `make package`
+```
+
 **CI runs `make watchapp` too** — `.gitea/workflows/build.yml` builds
 and tests everything inside a container built from `build-image/`,
 which bundles the Pebble SDK alongside the C toolchain so the runner