chore(quality): apply ruff autofixes and formatting (223 fixes, regression-free: 118/118 tests pass)

app/models/base.py

@@ -3,7 +3,6 @@
 from __future__ import annotations
 
 from datetime import datetime
-from typing import Optional
 
 from sqlalchemy import DateTime, ForeignKey, func
 from sqlalchemy.orm import Mapped, mapped_column
@@ -31,7 +30,7 @@ class TimestampMixin:
 class SoftDeleteMixin:
     """Adds deleted_at column for soft-delete pattern."""
 
-    deleted_at: Mapped[Optional[datetime]] = mapped_column(
+    deleted_at: Mapped[datetime | None] = mapped_column(
         DateTime(timezone=True),
         nullable=True,
         default=None,