Fix CI failures: add backend/conftest.py for module resolution and run black formatting

- Add backend/conftest.py that inserts the backend directory into sys.path,
  fixing ModuleNotFoundError when pytest runs from the backend/ directory
  (as CI does with `cd backend && pytest tests/`)
- Run black formatter on all 28 backend files that needed reformatting
- All 53 tests pass with both `pytest tests/` and `python -m pytest tests/`

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
Agent-Logs-Url: https://github.com/christianlouis/pop_puller_to_gmail/sessions/beb47db2-da25-416a-8fb0-c1452a3b22a7

backend/app/api/v1/endpoints/notifications.py

@@ -1,4 +1,5 @@
 """Notification configuration endpoints"""
+
 from typing import List
 from fastapi import APIRouter, Depends, HTTPException, status
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -8,23 +9,24 @@ from app.core.database import get_db
 from app.core.deps import get_current_active_user
 from app.models.database_models import User, NotificationConfig
 from app.models.schemas import (
-    NotificationConfigCreate, NotificationConfigResponse, NotificationConfigUpdate
+    NotificationConfigCreate,
+    NotificationConfigResponse,
+    NotificationConfigUpdate,
 )
 
 router = APIRouter()
 
 
-@router.post("", response_model=NotificationConfigResponse, status_code=status.HTTP_201_CREATED)
+@router.post(
+    "", response_model=NotificationConfigResponse, status_code=status.HTTP_201_CREATED
+)
 async def create_notification_config(
     config_in: NotificationConfigCreate,
     current_user: User = Depends(get_current_active_user),
-    db: AsyncSession = Depends(get_db)
+    db: AsyncSession = Depends(get_db),
 ):
     """Create notification configuration"""
-    config = NotificationConfig(
-        user_id=current_user.id,
-        **config_in.dict()
-    )
+    config = NotificationConfig(user_id=current_user.id, **config_in.dict())
     db.add(config)
     await db.commit()
     await db.refresh(config)
@@ -34,7 +36,7 @@ async def create_notification_config(
 @router.get("", response_model=List[NotificationConfigResponse])
 async def list_notification_configs(
     current_user: User = Depends(get_current_active_user),
-    db: AsyncSession = Depends(get_db)
+    db: AsyncSession = Depends(get_db),
 ):
     """List all notification configurations"""
     result = await db.execute(