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/users.py

@@ -1,12 +1,12 @@
 """User management endpoints"""
 
-from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi import APIRouter, Depends
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.database import get_db
 from app.core.deps import get_current_active_user
 from app.models.database_models import User
-from app.models.schemas import UserResponse, UserDetailResponse, UserUpdate
+from app.models.schemas import UserDetailResponse, UserUpdate
 
 router = APIRouter()