fix(ui,player): scroll restore, immersive fullscreen, watched toggle, handoff timeline, PiP

Batch of reported bugs and enhancements.

UI
- Pages no longer inherit the previous page's scroll position (DR-156, UR-072).
  The shell keeps its scrollers alive across navigation by design, so the
  element never remounts and its scrollTop survived the route change; SvelteKit
  restores window scroll, which this app never uses. ScrollMemory records the
  offset per route and per container: forward moves reset to the top, Back
  restores where the route was left.
- Season header stacks on narrow screens, and the title span gets min-w-0 so it
  actually truncates instead of overflowing under the action buttons.
- Favourites gets a labelled tile at the head of the library grid rather than
  only an unlabelled heart icon in the header.

Playback
- Full-screen video on Android hides the system bars (DR-157, UR-066).
  requestFullscreen() cannot touch the Activity window from inside a WebView, so
  the control did nothing visible while the bars stayed painted over the video.
  ImmersiveModeBridge hides them, restored on exit, Escape and teardown.
- Background-audio handoff stops leaking its relative timeline (DR-159).
  background_audio_base was a display-only correction applied in two places
  while progress reports to Jellyfin, the frontend and media3's own seeks all
  worked in the relative timeline treating it as absolute — each crossing losing
  exactly `base` seconds. The conversion now happens once, in the position tick,
  and inbound seeks resolve through seek_absolute, which re-opens the stream at
  the requested position because the handoff transcode cannot seek.
- Picture-in-picture works on the path that actually plays video (DR-160).
  canEnterPip demanded a native ExoPlayer surface, but that path is behind a
  flag defaulting to off, so PiP could never engage. It now accepts the WebView
  <video> too, keeping the WebView visible and routing play/pause to the element.
- Native video is now the default so PiP has a real surface (DR-161). The
  scrub-regression tests pinned the flag-off path implicitly; they now mock it
  off explicitly. The native scrub/seek path is not covered by the suite and
  needs device verification.

Watched state
- Watched toggle on the episode row, season header, series and movie hero, and
  the Episode Focus View (DR-158, UR-073). Both backend halves already existed
  with no caller. storage_set_watched covers a container's episodes so the
  toggle is honest offline, and QueuedOp::MarkUnplayed gives the sync queue the
  missing direction.

Release
- Fix the Android versionCode floor (set-version.sh). v0.5.2 shipped code 5002
  under an earlier minor*1000 scheme, but the current minor*100 formula yields
  1502 for that version and 1503 for 0.5.3 — so every 0.5.x release built from
  it was an un-installable downgrade for anyone already on v0.5.2. Widened to
  10000 + major*1000000 + minor*1000 + patch (0.5.3 -> 15003).
- Bump to 0.5.3.

src-tauri/src/commands/player/mod.rs

@@ -770,22 +770,23 @@ pub async fn player_enter_background_audio(
 pub async fn player_exit_background_audio(
     player: State<'_, PlayerStateWrapper>,
 ) -> Result<f64, String> {
-    // Back to foreground playback: the lockscreen scrubber is absolute again.
-    let _ = crate::player::set_lockscreen_position_offset(0.0);
-
     let controller = player.0.lock().await;
-    // The base offset (handoff position) + native player's relative position =
-    // the absolute position to resume the video at. Zero after a backend-driven
-    // episode advance, whose stream already starts at its own zero.
-    let base = controller.exit_background_audio();
-    // Capture position into a `let` BEFORE stop() — never hold work across a lock
-    // re-entrant call (deadlock discipline, CLAUDE.md).
-    let relative = controller.position();
+
+    // Read the position BEFORE clearing either base. The position tick applies the
+    // base natively, so a tick landing between "base cleared" and "position read"
+    // would hand back a relative position — the whole bug, reintroduced at the one
+    // moment it matters most. Capturing into a `let` before stop() is also the
+    // lock discipline from CLAUDE.md: never hold work across a re-entrant call.
+    // (DR-159)
+    let absolute = controller.position();
+
+    // Now safe to tear the handoff down, native side first.
+    let _ = crate::player::set_lockscreen_position_offset(0.0);
+    controller.exit_background_audio();
     controller.stop().map_err(|e| e.to_string())?;
-    let absolute = base + relative;
     info!(
-        "player_exit_background_audio: base={:.1}s + relative={:.1}s = {:.1}s",
-        base, relative, absolute
+        "player_exit_background_audio: resuming the video at {:.1}s",
+        absolute
     );
     Ok(absolute)
 }
@@ -1207,9 +1208,12 @@ pub async fn player_seek(
         let position_ticks = (position * 10_000_000.0) as i64;
         client.session_seek(session_id, position_ticks).await?;
     } else {
-        // Local playback
+        // Local playback. seek_absolute, not seek: the position came from the UI,
+        // which shows the whole item, so during a background-audio handoff it has
+        // to be resolved against the episode's timeline rather than the handoff
+        // stream's. (DR-159)
         let controller = player.0.lock().await;
-        controller.seek(position).map_err(|e| e.to_string())?;
+        controller.seek_absolute(position).await?;
     }
 
     let controller = player.0.lock().await;