Add mobile message image galleries (#3312)

## What
- group uploaded photos into full-width message carousels
- add a fullscreen viewer with pinch zoom, double-tap reset, swipe-down
dismissal, a centered filmstrip, and image actions
- preload nearby display-sized images for smoother swiping and keep each
upload as its own avatar-backed message

## Validation
- `just mobile-check`
- `flutter test test/features/channels/message_content_test.dart`
- iOS 26.5 simulator gesture pass

---------

Signed-off-by: kenny lopez <klopez4212@gmail.com>

mobile/android/app/src/main/AndroidManifest.xml

@@ -1,6 +1,15 @@
-<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+<manifest
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools">
     <uses-permission android:name="android.permission.INTERNET" />
     <uses-permission android:name="android.permission.CAMERA" />
+    <uses-permission
+        android:name="android.permission.READ_EXTERNAL_STORAGE"
+        android:maxSdkVersion="28"
+        tools:replace="android:maxSdkVersion" />
+    <uses-permission
+        android:name="android.permission.WRITE_EXTERNAL_STORAGE"
+        android:maxSdkVersion="28" />
     <application
         android:label="@string/app_name"
         android:name="${applicationName}"

mobile/android/app/src/main/kotlin/xyz/block/buzz/mobile/MainActivity.kt

@@ -97,6 +97,9 @@ class MainActivity : FlutterActivity() {
                     TRANSCODE_VIDEO_TO_MP4_METHOD -> {
                         handleTranscodeVideoToMp4(call.arguments, result)
                     }
+                    REQUIRES_LEGACY_MEDIA_STORAGE_PERMISSION_METHOD -> {
+                        result.success(Build.VERSION.SDK_INT <= Build.VERSION_CODES.P)
+                    }
                     else -> result.notImplemented()
                 }
             }
@@ -284,5 +287,7 @@ class MainActivity : FlutterActivity() {
         private const val SANITIZE_IMAGE_FOR_UPLOAD_METHOD = "sanitizeImageForUpload"
         private const val TRANSCODE_IMAGE_TO_JPEG_METHOD = "transcodeImageToJpeg"
         private const val TRANSCODE_VIDEO_TO_MP4_METHOD = "transcodeVideoToMp4"
+        private const val REQUIRES_LEGACY_MEDIA_STORAGE_PERMISSION_METHOD =
+            "requiresLegacyMediaStoragePermission"
     }
 }