fix: remove pycache and .env from git tracking

These files are listed in .gitignore but were accidentally committed.
Removing them from git while keeping them locally.

src/backend/.env

@@ -1,11 +0,0 @@
-DATABASE_URL=sqlite:///./data/app.db
-SECRET_KEY=your-super-secret-key-change-in-production
-JWT_ALGORITHM=HS256
-ACCESS_TOKEN_EXPIRE_MINUTES=1440
-MINIMAX_API_KEY=your-minimax-api-key
-MINIMAX_MODEL=MiniMax-Text-01
-AVE_API_KEY=your-ave-cloud-api-key
-AVE_API_PLAN=free
-HOST=0.0.0.0
-PORT=8000
-DEBUG=false