feat: add groq fallback to gemini agent calls

feat: add 3-layer prompt guard security module

feat: implicit login after signup

chore: restrict file upload module to supported file types

feat: Add authentication security & prompt injection defenses

Add safe error handling to Supabase auth and session endpoints

Improve UI error handling with user-friendly statements instead of raw tracebacks

Add Image/Scan OCR support with Groq fallback

Fix Supabase stale connection and add HF Space CI/CD

Patched OAuth redirect URI for production

Initial commit: Multi-User AI Study Agent