[codex] Add subtitle QA review tool

[laubonghaudoi]

Summary

• Adds a browser-only subtitle QA engine for common cleanup issues.
• Adds a compact header-launched QA dialog with severity/rule filters, threshold controls, previews, and selected automatic fixes.
• Wires fixes through the existing active-track replaceAllSubtitlesAction path so one apply operation remains undoable.
• Adds English, German, and Cantonese UI strings plus rule coverage in tests/subtitle-quality.test.ts.

Closes #33.

Validation

• npm run lint
• npm test (55 passing tests)
• npm run build

Notes

• The local .codex/ environment file is intentionally not included.
• The QA tool stays scoped to the active track and browser-only deterministic subtitle data logic.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	subtitle-editor	77c84ca	Commit Preview URL Branch Preview URL	Apr 24 2026, 03:30 PM