Title: File Upload & Document Management Endpoint

[kmuwanga83]

Description:
Allow users to upload documents / files (images, pdf, etc.) associated with entities via backend APIs.

Checklist:

• Endpoint for file upload
• File size / type validation
• Storage solution (local filesystem, cloud, etc.)
• Endpoint to fetch / download files
• Security / access controls
• Clean up orphaned files

Labels: backend feature file-upload