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/schemas/winbox_remote.py

@@ -57,6 +57,7 @@ class RemoteWinboxDuplicateDetail(BaseModel):
 
 class RemoteWinboxSessionItem(BaseModel):
     """Used in the combined active sessions list."""
+
     session_id: uuid.UUID
     status: RemoteWinboxState
     created_at: datetime