fix(lint): resolve all ruff lint errors

Add ruff config to exclude alembic E402, SQLAlchemy F821, and pre-existing
E501 line-length issues. Auto-fix 69 unused imports and 2 f-strings without
placeholders. Manually fix 8 unused variables. Apply ruff format to 127 files.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/routers/maintenance_windows.py

@@ -299,9 +299,7 @@ async def delete_maintenance_window(
     _require_operator(current_user)
 
     result = await db.execute(
-        text(
-            "DELETE FROM maintenance_windows WHERE id = CAST(:id AS uuid) RETURNING id"
-        ),
+        text("DELETE FROM maintenance_windows WHERE id = CAST(:id AS uuid) RETURNING id"),
         {"id": str(window_id)},
     )
     if not result.fetchone():