Implement video chunking for large file uploads

[clencyc]

Description

Large video uploads fail or timeout. Implement chunked uploads that split videos into smaller pieces and reassemble them server-side.

Acceptance Criteria

• Frontend splits files into 5MB chunks
• Upload each chunk separately with sequence number
• Backend receives chunks and stores temporarily
• Server reassembles chunks when all received
• Progress callback reports total upload %
• Handles network interruptions with retry logic
• Cleans up temporary files after reassembly
• Tested with videos > 100MB

Implementation Details

• Backend endpoint: POST /api/upload/chunk
• Request format: multipart with fields: chunk_data, chunk_number, total_chunks, upload_id
• Response: {"chunk_index": 0, "status": "received"}
• Final endpoint: POST /api/upload/complete?upload_id=xyz

Files to Modify

• Backend: LiveEditBackend/app.py - add chunk handlers
• Frontend: services/gemini.ts - add chunk upload logic
• Create: services/uploadManager.ts - handle chunking

Difficulty: Hard

Estimated time: 5-6 hours