fix(player): stack bilingual subtitle cues so they don't overlap

[ModerRAS]

Problem

Bilingual (CN+JP) ASS subtitles rendered as two overlapping layers because every dialogue cue shared the bottom-centre position and the renderers drew them on top of each other. With many simultaneous lines the stack also overflowed the screen and clipped every line to half-height.

Fix — both backends

ExoPlayer / media3 (default backend)

Subtitles were rendered by the PlayerView's built-in SubtitleView with no cue processing, so cues kept their ASS positions and collided.

• Intercept Player.Listener.onCues(CueGroup) in PlayerScreen to collect current cues.
• restackSubtitleCues(cues) (pure fn): assign explicit line numbers counting up from the bottom (-1, -2, … with LINE_TYPE_NUMBER + ANCHOR_TYPE_END) so cues stack without overlapping; clear embedded horizontal position/size (DIMEN_UNSET) so nothing drifts off-screen → fixes overflow; cap the stack at 4 (keeping most recent) so it never overflows the top → fixes clipping; preserves ASS embedded styling (colours/typeface) via buildUpon().
• Hide PlayerView.subtitleView; render a controlled SubtitleView overlay with the restacked cues, applying the existing transparent-background preference.

mpv / libass (experimental embedded backend)

• Set sub-ass-override=force in MiruMpvSurfaceView.initOptions() so libass ignores embedded ASS \pos/styles and renders plain, wrapped, bottom-stacked subtitles via its default collision avoidance → bilingual lines stack instead of overlapping.
• Declarative mpvSubtitleLayoutNormalisationOptions config (applied in initOptions).
• Note: this discards ASS styling (colours/fonts) on the mpv backend, trading fidelity for readability — consistent with normalising layout. Can be made a preference later if styled ASS is desired.

Tests

• SubtitleCueLayoutTest (6 tests, ExoPlayer restack logic) — all passing.
• MpvSubtitleLayoutTest (2 tests, mpv normalisation option) — all passing.
• Local: :ui-tv:testDebugUnitTest and :player-mpv-android:testDebugUnitTest both BUILD SUCCESSFUL (no regressions).

Notes

• Needs on-device verification of actual rendering (line spacing for multi-line cues is approximate; single-line-per-cue stacking is exact).
• ExoPlayer path keeps ASS colours; mpv path uses plain style (libass force).

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⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

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Run ID: a78fef62-a15d-4dc0-93f4-21d1fda4f255

📥 Commits

Reviewing files that changed from the base of the PR and between 4fc2fb6 and 66e956d.

📒 Files selected for processing (6)

• player-mpv-android/src/main/kotlin/is/xyz/mpv/MiruMpvSurfaceView.kt
• player-mpv-android/src/main/kotlin/is/xyz/mpv/MpvSubtitleLayout.kt
• player-mpv-android/src/test/kotlin/is/xyz/mpv/MpvSubtitleLayoutTest.kt
• ui-tv/src/main/kotlin/com/miruplay/tv/ui/player/PlayerScreen.kt
• ui-tv/src/main/kotlin/com/miruplay/tv/ui/player/SubtitleCueLayout.kt
• ui-tv/src/test/kotlin/com/miruplay/tv/ui/player/SubtitleCueLayoutTest.kt

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