feat: English locale, agent language routing, SRT import, transcript diagnostics, cleanup controls, and editor improvements

[matthewdonsemail-lab]

Summary

Comprehensive editor improvements accumulated during local development: English locale default, agent language routing, SRT file import, transcript diagnostics, cleanup controls, and various editor/timeline/audio/captions/GL/export enhancements.

Changes

Locale and Agent

• English locale default for first-run (saved Chinese preference preserved)
• Agent language routing via agentLanguagePrompt(locale) for locale-aware responses
• Prompt enhancement writes in selected interface language
• English transcript/SRT/diagnostic translations

Transcription

• Transcript extraction/source loading/upload/processing progress phases with timestamped detail
• clearGeneratedTranscripts() and clearAllCaptions() cleanup controls
• SRT file import with UTF-8 BOM, CRLF/LF, comma/period fractions, multiline cues, HTML tag stripping
• Imported SRT captions create editable manual caption data via newManualCaptions()
• SRT import moved from Subtitles/Captions panel to Transcript toolbar

Infrastructure

• Docker compose and .dockerignore for container deployment
• Removed unused transition preview/audio files
• Removed community section from READMEs

Editor

• Various editor, timeline, audio, captions, GL, and export improvements
• Full test suite and lint pass

Verification

• npm run lint — passed
• npm test — full suite passed
• npm run build — production build succeeded

Security

No credentials or .env.local files are included. All changes are source code and documentation only.

[0xsline]

@matthewdonsemail-lab, thank you for putting this together. main has advanced to ecd5a3c, and the current PR touches 307 files across several unrelated surfaces, so we cannot merge it safely in its current form.

Please rebase on the latest main and split the work into focused PRs:

1. Locale and Agent language routing
2. SRT, transcription, and cleanup controls
3. Docker and deployment configuration

For each PR, remove unrelated comment translation/formatting churn and delete the .bak-* files. The Docker configuration must not hard-code 100.98.241.63:15199; use a portable, configurable binding. Please leave transition preview/audio deletions, README/community asset removals, and unrelated editor changes out unless they are submitted separately with rationale and coverage.

Each replacement PR needs npx tsc --noEmit, npm test, and npm run build; Agent/preview changes also need one browser end-to-end run on localhost:5199. Please keep #17 open and link the replacement PRs here so we can re-review them against the updated main.