feat(subtitles): add regex subtitle filters with built-in presets (#318)

- Add `subtitleFilter` config with four presets: parentheses, brackets, speaker prefix and music symbols. Custom regex rules run after the presets.
- Filter primary text where it enters the app (live `sub-text` and parsed cues), so the overlay, sidebar, mining and stats all get the same filtered text.
- Changes hot-reload: the current line is read again and the active track is parsed again, using the filter config as the prefetch parse key.
- Add a custom rule editor in Settings under Behavior → Subtitle Filters that checks patterns as you type.
- Update the config example, the configuration docs and the architecture domains doc, and add a changelog fragment.

docs/architecture/domains.md

@@ -36,6 +36,7 @@ Read when: you need to find the owner module for a behavior or test surface
   Windows executable lookup and detached process creation are shared in `src/main/runtime/mpv-process.ts`. The Windows launcher and Jellyfin handlers retain their own playback and connection workflows.
 - Subtitle/token pipeline: `src/core/services/subtitle-*.ts`, `src/core/services/tokenizer*`, `src/core/services/tokenizer/`, `src/subsync/`
   JLPT and frequency annotation lookups: `src/main/jlpt-runtime.ts`, `src/main/frequency-dictionary-runtime.ts`, assembled by `src/main/assemblies/dictionaries.ts`
+  Subtitle text filters (`subtitleFilter`): `src/shared/subtitle-text-filter.ts`. Primary text is filtered at its two entry points, live `sub-text` in `mpv-protocol.ts` and parsed cues in `playback.ts`, so every consumer sees the same text and live/cue matching still works. A config change re-reads `sub-text` and re-parses the active track (the prefetch controller's parse key).
 - First-run setup: `src/main/runtime/first-run-setup-*.ts`, assembled by `src/main/assemblies/first-run-setup.ts`
 - Anki workflow: `src/anki-integration/`, `src/core/services/anki-jimaku*.ts`
   Card mining handlers, the pending lookup context, field grouping, and media timing review wiring: