feat: enforce file checks on client-side

Objective: Fail-fast validation and bandwidth optimization.

Description: To fail fast and save bandwidth, the CLI should enforce basic file validation before attempting to upload to the FastAPI backend.

• Implement file size limits (os.path.getsize) matching the server's rules (e.g., audio, video, image size limits as defined in app/schemas/validation.py).
• Validate file extensions and MIME types locally before uploading.
• Ensure text content lengths and metadata fields (like title, description) adhere to the backend's minimum/maximum constraints.