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/market_widgets.dart

@@ -36,6 +36,7 @@ class OfferThumbnail extends StatelessWidget {
     return ClipRRect(
       borderRadius: BorderRadius.circular(10),
       child: _offerImage(
+        context,
         url,
         semanticLabel: semanticLabel,
         width: size,
@@ -63,7 +64,7 @@ class OfferHeroImage extends StatelessWidget {
       borderRadius: BorderRadius.circular(14),
       child: AspectRatio(
         aspectRatio: 4 / 3,
-        child: _offerImage(url, semanticLabel: semanticLabel),
+        child: _offerImage(context, url, semanticLabel: semanticLabel),
       ),
     );
   }
@@ -73,6 +74,7 @@ class OfferHeroImage extends StatelessWidget {
 /// remote URL (via network), always cropping to fill and falling back to a
 /// neutral placeholder — a broken image must never block the card.
 Widget _offerImage(
+  BuildContext context,
   String url, {
   required String semanticLabel,
   double? width,
@@ -80,10 +82,16 @@ Widget _offerImage(
 }) {
   final inline = decodeDataUri(url);
   if (inline != null) {
+    // For a sized thumbnail, decode down to its on-screen pixels instead of the
+    // photo's full resolution (Play's "bitmap downscaling"). The hero image
+    // passes no width, so it decodes at native size as intended.
+    final dpr = MediaQuery.devicePixelRatioOf(context);
     return Image.memory(
       inline,
       width: width,
       height: height,
+      cacheWidth: width == null ? null : (width * dpr).round(),
+      cacheHeight: height == null ? null : (height * dpr).round(),
       fit: BoxFit.cover,
       semanticLabel: semanticLabel,
       errorBuilder: (context, _, _) =>