perf(android): R8, bitmap downscaling, edge-to-edge; recover device compat; publish to production

Device compatibility (regression fix):
- The CAMERA permission (from zxing_barcode_scanner / image_picker) implicitly
  required android.hardware.camera, excluding camera-less devices — Play showed
  Automotive -96%, Chromebook -86%, TV -25%. Declare camera & location
  uses-feature required="false" to keep those devices supported.
- Detect a real camera at runtime (PackageManager.FEATURE_CAMERA_ANY via the
  existing MethodChannel), cache it at bootstrap, and hide the QR scan button and
  the camera photo-source option when absent, so no broken actions are offered.

Play "app optimization" recommendations:
- Enable R8 (isMinifyEnabled + isShrinkResources) with keep rules for the
  OCR (tesseract4android), SQLCipher and notifications JNI/reflection code.
- Bitmap downscaling: cacheWidth/cacheHeight (and ResizeImage for avatars) on
  list thumbnails and avatars so photos decode to on-screen size, not full res.
- Edge-to-edge: opt in with transparent system bars in main().

Release flow:
- Tagged builds now publish to the production track at 100% (was internal);
  add a manual deploy_internal lane as a QA safety net.
- Document country/region availability as a Play Console setting (not in-repo).

apps/app_seeds/lib/ui/peer_avatar.dart

@@ -34,7 +34,19 @@ class PeerAvatar extends StatelessWidget {
     if (pic.startsWith('data:')) {
       final bytes = decodeDataUri(pic);
       if (bytes != null) {
-        return CircleAvatar(radius: radius, backgroundImage: MemoryImage(bytes));
+        // Decode the photo down to the avatar's on-screen size (in physical
+        // pixels) instead of full resolution — the "bitmap downscaling" Play
+        // recommends. A tiny disc never needs a multi-megapixel decode.
+        final side = (radius * 2 * MediaQuery.devicePixelRatioOf(context))
+            .round();
+        return CircleAvatar(
+          radius: radius,
+          backgroundImage: ResizeImage(
+            MemoryImage(bytes),
+            width: side,
+            height: side,
+          ),
+        );
       }
     } else if (pic.startsWith(avatarGlyphPrefix)) {
       final glyph = avatarGlyphChar(pic.substring(avatarGlyphPrefix.length));