ci: add ruff linting and mypy type checking

Add ruff and mypy to dev dependencies with configuration in pyproject.toml.
Add a lint CI job that runs ruff check, ruff format --check, and mypy.
Auto-fix import sorting and formatting across the codebase. Exclude
alembic/versions from linting (auto-generated migrations). Ignore B008
(FastAPI Depends pattern) and RUF001 (unicode in user-facing strings).

21 ruff lint errors and 50 mypy errors remain for manual review.

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

app/auth/service.py

@@ -21,9 +21,7 @@ class AuthService:
         normalized_email = email.strip().lower()
         if not normalized_email or not password:
             return None
-        result = await db_session.execute(
-            select(User).where(User.email == normalized_email)
-        )
+        result = await db_session.execute(select(User).where(User.email == normalized_email))
         user = result.scalar_one_or_none()
         if user is None or not user.is_active:
             return None