fix(android): draw the subtitles the player already decodes

Turning a subtitle on did nothing even after DR-259 made them load. ExoPlayer
decodes subtitles and delivers them to a listener; it draws none itself. A
PlayerView would supply the view that does, but native video here is a bare
TextureView the WebView composites over — so nothing held the cues and every
one was decoded, delivered and dropped. There was no onCues, no TextOutput and
no SubtitleView anywhere in the app, and media3-ui was not even a dependency.

The gap was invisible for as long as every subtitle URL 404ed: with no text
track to select there was never a cue to lose, so fixing the URL is what
exposed it.

media3-ui's SubtitleView now takes each CueGroup and is attached at index 1 of
the content view — above the video, still below the WebView, so cues sit over
the picture and under the app's own controls. It is fitted to the letterboxed
video rect rather than the screen, so cues stay inside the picture and follow
it on rotation, and is removed by the same teardown that detaches the surface
(the defect DR-184 exists to prevent).

Verified on a device: track selected with no "Invalid subtitle track index",
SubtitleView attached at the fitted rect per the live view hierarchy, and cues
legible on screen during playback.

TRACES: UR-020, UR-003 | DR-260

CHANGELOG.md

@@ -9,6 +9,19 @@ generated trace matrix lives in [docs/traceability.md](docs/traceability.md).
 For how long each fixed defect had been shipping before it was found, see
 [docs/defect-windows.md](docs/defect-windows.md).
 
+## Unreleased
+
+### 🐛 Fixes
+
+- **Subtitles appear on screen on Android.** Turning one on did nothing, even
+  once they were loading again: the player hands finished subtitles to a view
+  that draws them, and on the native Android path there was no such view — so
+  every cue was decoded, delivered and dropped. There is one now, sitting over
+  the picture and under the controls, following the video's shape when the
+  screen turns. This was hidden behind the loading failure fixed in v0.11.1;
+  with nothing to select, there had never been a cue to lose. (UR-020, UR-003 →
+  DR-260)
+
 ## v0.11.1
 
 Four fixes. Two had been present since the first release and were found on a