Fix Quest launch crashes, version the APK like the tarball, and support native builds in Android Studio

- patchelf gl4es's embedded SONAME to libGL.so so AGP's jniLibs packaging
  (which drops any file not literally named "*.so") and the dynamic
  linker's NEEDED-entry resolution (by embedded SONAME, not filename)
  finally agree - fixes the "library \"libGL.so.1\" not found" crash seen
  on real Quest hardware.
- QuestShockActivity now checks that res/data and res/sound exist before
  starting the native engine, showing an explanatory dialog instead of
  crashing on init_popups' unchecked NULL resource load when a fresh
  install has no game data copied in yet.
- dist/questshock-<version>-android-arm64.apk is now versioned from the
  same git-tag-or-dev-placeholder scheme as the desktop tarball
  (build-image/version.sh, shared by both via the Makefile and
  build-apk.sh).
- build-image/prepare-android-project.sh (prep logic extracted out of
  build-apk.sh) can now stage android/ for a native build directly in
  Android Studio (--host-paths), exporting the prebuilt SDL2/SDL2_mixer/
  fluidsynth-lite/gl4es libraries and writing host-resolvable paths,
  instead of only ever building inside the Docker image.
- Corrected GET_ASSETS.txt/GET_ASSETS_QUEST.txt, which wrongly described
  merging res/pc/hd and res/pc/cdrom trees out of the raw installer's
  sshock.kpf - an already-installed copy's res/data res/sound can just
  be copied directly, with extract_assets.sh only needed from the raw
  installer.

android/app/src/main/java/de/ladkau/questshock/QuestShockActivity.java

@@ -1,6 +1,7 @@
 package de.ladkau.questshock;
 
 import android.Manifest;
+import android.app.AlertDialog;
 import android.content.pm.PackageManager;
 import android.content.res.AssetManager;
 import android.os.Bundle;
@@ -96,6 +97,18 @@ public class QuestShockActivity extends SDLActivity {
             copyAssetFile("GET_ASSETS_QUEST.txt", marker);
         }
 
+        // Shockolate's engine/ is never patched to check this itself (see the
+        // class doc above) - it just does plain fopen("res/data/...", ...)
+        // and, on a fresh install with no game data copied in yet, that
+        // fails deep inside startup (init_popups(), which doesn't NULL-check
+        // the load) as a hard native crash instead of a message. Catch the
+        // missing-data case here instead, before super.onCreate() ever
+        // starts Shockolate's native main().
+        if (!isNonEmptyDir(new File(gameDir, "res/data")) || !isNonEmptyDir(new File(gameDir, "res/sound"))) {
+            showMissingAssetsDialog();
+            return;
+        }
+
         // chdir() is process-wide, not per-thread - already in effect for
         // every thread (including the one that will run Shockolate's own
         // SDL_main) by the time super.onCreate() below starts it.
@@ -104,6 +117,40 @@ public class QuestShockActivity extends SDLActivity {
         super.onCreate(mSavedInstanceState);
     }
 
+    private static boolean isNonEmptyDir(File dir) {
+        String[] entries = dir.list();
+        return entries != null && entries.length > 0;
+    }
+
+    // Same single-button, non-cancelable pattern as SDLActivity's own
+    // "broken libraries" dialog (org/libsdl/app/SDLActivity.java) - there's
+    // no game to start without this data, so the only way forward is to
+    // close, copy the assets, and relaunch. Message text mirrors
+    // res/assets/GET_ASSETS_QUEST.txt (also extracted to GAME_DIR) so the
+    // user isn't sent hunting for a second file just to read it the first
+    // time - it points back there at the end in case they need it again.
+    private void showMissingAssetsDialog() {
+        new AlertDialog.Builder(this)
+            .setTitle("Game data missing")
+            .setMessage("This app does not include System Shock's game data - it's "
+                + "copyrighted, proprietary content that can't be redistributed. To "
+                + "play, you need to own a copy of System Shock: Enhanced Edition (e.g. "
+                + "from gog.com), installed (on Windows, or via Wine/Proton on Linux).\n\n"
+                + "Using SideQuest (or any MTP file browser) with your Quest connected, "
+                + "copy its res/data/ and res/sound/ folders directly into:\n"
+                + GAME_DIR + "/res/data/\n"
+                + GAME_DIR + "/res/sound/\n"
+                + "They already contain everything needed, in the right layout - no "
+                + "merging or extraction required.\n\n"
+                + "Then relaunch.\n\n"
+                + "(These instructions are also in GET_ASSETS_QUEST.txt in the "
+                + "questshock folder on this device, if you need to read them again.)")
+            .setCancelable(false)
+            .setPositiveButton("Exit", (dialog, which) -> finish())
+            .create()
+            .show();
+    }
+
     private void copyAssetFile(String assetPath, File dest) {
         if (dest.exists()) {
             return;