Backend Enhancements: Migrations, API Development, RBAC, Celery Integration, File Uploads, and Cleanup

[NallaAvanthika]

1. Added new fields and created migrations for conversation and file models.
2. Developed API endpoints for:

• Retrieving conversation summaries with pagination and filtering.
• Uploading files with duplication checks
• Listing uploaded files along with their metadata.
• Deleting files securely.

3. Implemented role-based access control to restrict file management operations.
4. Configured Celery for background task processing and scheduled periodic cleanup of old conversations.
5. Created Django management commands to handle data cleanup tasks.
6. Enhanced logging to track file uploads, deletions, and accesses.
7. Added unit and integration tests to ensure the stability of new features.
8. Migrated the database from SQLite to PostgreSQL, including necessary schema updates.

Please review and share any feedback or suggestions.