feat(auth): Complete OIDC security refactor and modernize test suite

- Refactored OIDC flow to implement PKCE, state/nonce validation, and BFF pattern.
- Centralized configuration in Settings class (DEV_MODE, FRONTEND_URL, OIDC_REDIRECT_URI).
- Updated auth routers to use conditional secure cookie flags based on DEV_MODE.
- Modernized and cleaned up test suite by removing legacy Streamlit tests.
- Fixed linting errors and unused imports across the backend.

backend/.env.example

@@ -6,7 +6,8 @@ GOOGLE_API_KEY=your_google_api_key_here
 DATA_DIR=data
 DATA_STATE=new_jersey
 LOG_LEVEL=INFO
-DEV_MODE=false
+DEV_MODE=true
+FRONTEND_URL=http://localhost:5173
 
 # Security & JWT Configuration
 SECRET_KEY=change-me-in-production
@@ -28,7 +29,7 @@ HISTORY_DB_URL=postgresql://user:password@localhost:5433/ea_history
 OIDC_CLIENT_ID=your_client_id
 OIDC_CLIENT_SECRET=your_client_secret
 OIDC_SERVER_METADATA_URL=https://your-authentik.example.com/application/o/ea-chatbot/.well-known/openid-configuration
-OIDC_REDIRECT_URI=http://localhost:8501
+OIDC_REDIRECT_URI=http://localhost:8000/api/v1/auth/oidc/callback
 
 # Node Configuration Overrides (Optional)
 # Format: <NODE_NAME>_LLM__<PARAMETER>