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>
Agent-Logs-Url: https://github.com/christianlouis/pop_puller_to_gmail/sessions/99c3a25f-3479-473d-ac95-9faaa0ddd55b

backend/alembic/env.py

@@ -11,7 +11,7 @@ sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
 
 from app.core.config import settings
 from app.core.database import Base
-from app.models import database_models  # Import all models
+from app.models import database_models  # noqa: F401 - Import all models for Alembic
 
 # this is the Alembic Config object
 config = context.config