Fix all 33 ruff linting errors causing CI failures

- Remove unused imports (F401) across 17 files
- Fix f-strings without placeholders (F541) in 3 files
- Add noqa: E712 to SQLAlchemy == True comparisons (valid ORM pattern)
- Preserve alembic side-effect import with noqa: F401

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
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backend/app/api/v1/endpoints/notifications.py

@@ -1,7 +1,7 @@
 """Notification configuration endpoints"""
 
 from typing import List
-from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi import APIRouter, Depends, status
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select
 
@@ -11,7 +11,6 @@ from app.models.database_models import User, NotificationConfig
 from app.models.schemas import (
     NotificationConfigCreate,
     NotificationConfigResponse,
-    NotificationConfigUpdate,
 )
 
 router = APIRouter()