feat(v0.12.3): F276-F305 video upload, HLS transcoding, education tests
- Add video upload endpoint POST /courses/:id/lessons/:lesson_id/video
- Add VideoTranscodeService for multi-bitrate HLS (720p/480p/360p)
- Add VideoTranscodeWorker for async lesson video processing
- Add SetLessonVideoPath and UpdateLessonTranscoding to education service
- Add uploadLessonVideo to frontend educationService with progress
- Add comprehensive handler tests (video upload, auth, validation)
- Add service-level tests (models, slugs, clamping, errors, UUIDs)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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