fix: apply PR#30 patches for upload bug and AssemblyAI SDK compatibility

[rodrigolopezguerra]

Summary

• Fix upload bug: add missing config = Config() in media.py
• Fix AssemblyAI SDK: update to 0.40+ for speech_models support
• Fix worker SSE disconnect handling
• Fix cleanup_settings dead code causing worker crash
• Add ultralytics for YOLOv8 pose detection (PR#30 feature)

Changes

• backend/pyproject.toml: assemblyai>=0.40.0, ultralytics>=8.0.0
• backend/src/api/routes/media.py: +1 line (config = Config())
• backend/src/workers/progress.py: SSE cleanup in try/except
• backend/src/workers/tasks.py: remove dead cleanup_settings param
• backend/src/video_utils.py: full PR#30 face tracking + SDK fix

Testing

• Upload video works (was: name 'config' is not defined)
• Worker no longer crashes on cleanup_settings
• AssemblyAI transcription uses correct speech_models API

Closes #30

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