Android picture-in-picture, and fix three dead Android config files

Add PiP for native (ExoPlayer) video on Android. Video renders into a
SurfaceView behind the WebView, so PiP is driven by the Activity shrinking
into a floating window rather than the HTML5 PiP API (which WebKitGTK does
not implement, hence Android-only).

- PictureInPictureManager.kt: enter PiP with the video's aspect ratio
  (clamped to the 1:2.39-2.39:1 range Android accepts, outside which it
  throws), plus a play/pause RemoteAction. Hides the WebView while in PiP -
  it is opaque and sits above the surface, so it would otherwise occlude the
  video entirely - and re-fits the surface on exit.
- MainActivity.kt: onUserLeaveHint auto-PiP, onPictureInPictureModeChanged,
  and an AndroidPictureInPicture JS interface following the existing
  AndroidAudioFocus pattern.
- pictureInPicture.ts + VideoPlayer.svelte: PiP button, rendered only when
  the native bridge reports support.
- proguard: keep rules for @JavascriptInterface methods, which are only
  referenced from JS and would be stripped in minified release builds.

Casting needs no special handling: canEnterPip() checks natively that a
local video surface is attached and playing, which a remote session lacks.

While wiring the manifest, found that three tracked files under
src-tauri/android/ were never reaching any build. Gradle reads only
gen/android/app/src/main/, and sync-android-sources.sh did not copy them:

- src/main/AndroidManifest.xml was a partial <application> fragment written
  as if Tauri merged it. It does not - there is no manifest-merger hook
  here, so its hardwareAccelerated flag never reached an APK. Promoted to
  the complete authoritative manifest (folding in that flag) and synced.
- src/main/res/values/themes.xml (transparent status bar, fitsSystemWindows)
  was never copied; the sync only globbed mipmap-*. Now synced.
- build.gradle.kts was a leftover com.android.library module config with
  stale media3 1.5.1 deps. The live deps are in app/build.gradle.kts at
  1.5.0. Deleted.

Verified: merged manifest now carries hardwareAccelerated,
supportsPictureInPicture, resizeableActivity and the density configChange;
themes.xml compiles into merged resources; Kotlin builds warning-free;
svelte-check clean; 537 frontend tests pass.

Not verified: PiP behaviour on a device, and the release keep rules against
a minified build. assembleUniversalDebug cannot complete in this
environment - the Rust step wants a dev-server addr file that only exists
under `tauri android dev`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/components/player/VideoPlayer.svelte

@@ -18,6 +18,7 @@
   import { playerController } from "$lib/player";
   import { Html5PlayerAdapter, type Html5ElementBridge } from "$lib/player/adapters";
   import { createRustReportHost } from "$lib/player/adapters/rustReportHost";
+  import { isPipSupported, enterPip } from "$lib/utils/pictureInPicture";
 
   interface Props {
     media: MediaItem | null;
@@ -1081,6 +1082,16 @@
     }
   }
 
+  // Resolved once at component setup: the PiP bridge is installed by
+  // MainActivity before the page loads and never changes for the session.
+  // Synchronous by design - no await in onMount (see VideoPlayer native-mode
+  // pitfalls: awaiting there flips the component into HTML5 mode).
+  const pipSupported = isPipSupported();
+
+  function handlePictureInPicture() {
+    enterPip();
+  }
+
   function toggleFullscreen() {
     if (!document.fullscreenElement) {
       document.documentElement.requestFullscreen();
@@ -1721,6 +1732,19 @@
         <!-- Volume Control -->
         <VolumeControl size="md" />
 
+        <!-- Picture-in-picture (Android only) -->
+        {#if pipSupported}
+          <button
+            onclick={handlePictureInPicture}
+            class="text-white hover:text-gray-300"
+            aria-label="Picture in picture"
+          >
+            <svg class="w-6 h-6" fill="currentColor" viewBox="0 0 24 24">
+              <path d="M19 11h-8v6h8v-6zm4 8V4.98C23 3.88 22.1 3 21 3H3c-1.1 0-2 .88-2 1.98V19c0 1.1.9 2 2 2h18c1.1 0 2-.9 2-2zm-2 .02H3V4.97h18v14.05z" />
+            </svg>
+          </button>
+        {/if}
+
         <!-- Fullscreen -->
         <button onclick={toggleFullscreen} class="text-white hover:text-gray-300" aria-label="Toggle fullscreen">
           <svg class="w-6 h-6" fill="currentColor" viewBox="0 0 24 24">