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>

tests/smoke/test_db_connectivity.py

@@ -20,4 +20,3 @@ async def test_database_connectivity_from_database_url() -> None:
             assert result.scalar_one() == 1
     finally:
         await engine.dispose()
-

tests/smoke/test_migration_schema.py

@@ -1,6 +1,6 @@
+import pytest
 from alembic.config import Config
 from alembic.script import ScriptDirectory
-import pytest
 from sqlalchemy import text
 from sqlalchemy.ext.asyncio import AsyncSession