feat(player): add transparent subtitle background option

[ModerRAS]

Summary

Add a per-player preference to render subtitles on a transparent background — only the text and outline are kept, and the black caption background is dropped.

Changes

• Preferences: PlaybackPreferencesManager persists subtitleBackgroundTransparent (default false); added to PlaybackPreferencesRepository.
• Player: PlayerScreen derives a CaptionStyleCompat with a transparent background when the option is on; PlayerViewModel exposes the state.
• Settings: PlaybackPanel gains a "透明底 / 黑色底" toggle.
• Web control: PlaybackSettingsDto/Request carry the flag; WebControlService get/set it; frontend App.vue adds the switch.

Tests

• PlaybackPreferencesManagerTest: preference persistence
• PlayerSubtitleStyleTest: caption style derivation keeps text/outline and only clears the background
• WebControlSettingsRouteTest: round-trip via the settings API

Notes

• Branch: feat/subtitle-transparent-background
• A stray NUL file in the repo root was left untracked intentionally (not part of this change).

Summary by CodeRabbit

• New Features

  • Added a subtitle setting to toggle transparent or black backgrounds.
  • Subtitle backgrounds now respect the selected preference during playback.
  • The setting is available in both the TV app and web control interface.
  • Preferences persist across sessions and synchronize through playback settings.

• Tests

  • Added coverage for preference persistence, subtitle styling, and web control synchronization.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 5dccfdb6-3dae-4a20-a43a-26f7fb8dc966

📥 Commits

Reviewing files that changed from the base of the PR and between 91dccbc and a23cb5c.

📒 Files selected for processing (14)

• core/model/src/main/kotlin/com/miruplay/tv/model/PlaybackUiConventions.kt
• data/src/main/kotlin/com/miruplay/tv/data/preferences/PlaybackPreferencesManager.kt
• data/src/test/kotlin/com/miruplay/tv/data/preferences/PlaybackPreferencesManagerTest.kt
• repository-api/src/main/kotlin/com/miruplay/tv/repository/PlaybackPreferencesRepository.kt
• ui-tv/src/main/kotlin/com/miruplay/tv/ui/player/PlayerScreen.kt
• ui-tv/src/main/kotlin/com/miruplay/tv/ui/player/PlayerViewModel.kt
• ui-tv/src/main/kotlin/com/miruplay/tv/ui/settings/AddSourceScreen.kt
• ui-tv/src/main/kotlin/com/miruplay/tv/ui/settings/SettingsViewModel.kt
• ui-tv/src/test/kotlin/com/miruplay/tv/ui/player/PlayerSubtitleStyleTest.kt
• ui-tv/src/test/kotlin/com/miruplay/tv/ui/settings/SettingsViewModelTokenTest.kt
• web-control-core/src/main/kotlin/com/miruplay/tv/webcontrol/WebControlModels.kt
• web-control-core/src/test/kotlin/com/miruplay/tv/webcontrol/WebControlSettingsRouteTest.kt
• web-control/frontend/src/App.vue
• web-control/src/main/kotlin/com/miruplay/tv/webcontrol/WebControlService.kt

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📝 Walkthrough

Walkthrough

The change adds a persisted subtitle background transparency preference. Android settings and the player use it, while web-control APIs and the frontend load and save it.

Changes

Subtitle background transparency

Layer / File(s)	Summary
Preference storage contract repository-api/src/main/kotlin/..., data/src/main/kotlin/..., data/src/test/...	The preference repository and SharedPreferences manager expose a Boolean setting that defaults to false. Tests verify persistence.
Android settings flow core/model/src/main/kotlin/..., ui-tv/src/main/kotlin/com/miruplay/tv/ui/settings/..., ui-tv/src/test/...	SettingsViewModel loads and saves the preference. PlaybackPanel provides localized labels, a toggle, and the current status.
Player subtitle rendering ui-tv/src/main/kotlin/com/miruplay/tv/ui/player/..., ui-tv/src/test/...	PlayerScreen applies system caption styles and optionally clears only the subtitle background. Tests verify style preservation.
Web-control settings flow web-control-core/src/main/kotlin/..., web-control/src/main/kotlin/..., web-control/frontend/src/..., web-control-core/src/test/...	Playback settings DTOs, service handling, frontend state, save requests, and route tests include subtitleBackgroundTransparent.

Estimated code review effort: 4 (Complex) | ~35 minutes

Sequence Diagram(s)

sequenceDiagram
  participant PlaybackPanel
  participant SettingsViewModel
  participant PlaybackPreferencesRepository
  participant PlaybackPreferencesManager
  participant PlayerViewModel
  participant PlayerScreen

  PlaybackPanel->>SettingsViewModel: setSubtitleBackgroundTransparent(value)
  SettingsViewModel->>PlaybackPreferencesRepository: set preference
  PlaybackPreferencesRepository->>PlaybackPreferencesManager: persist Boolean value
  PlayerViewModel->>PlaybackPreferencesRepository: get preference during initialization
  PlaybackPreferencesRepository-->>PlayerViewModel: return Boolean value
  PlayerViewModel-->>PlayerScreen: expose subtitleBackgroundTransparent
  PlayerScreen->>PlayerScreen: apply subtitleCaptionStyle

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Possibly related PRs

• ModerRAS/MiruPlay#46: Modifies adjacent subtitle settings infrastructure and shared playback preference components.
• ModerRAS/MiruPlay#50: Modifies playback preferences and settings APIs for a different playback option.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding a transparent subtitle background option for the player.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/subtitle-transparent-background

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