chore: enforce core ruff format gate

[earayu]

Summary

• sweep ruff formatting for the approved core surface: aperag/ + tests/
• expand make lint to check tests alongside aperag
• add tests/unit_test/test_format_drift.py as a unit guard for core format drift

Scope

• H1 only: aperag/ + tests/
• Not in scope: .github/utils/, scripts/, config/, models/, migration files

Gates

• uvx ruff format --check ./aperag ./tests -> 403 files already formatted
• uvx ruff check --no-fix ./aperag ./tests -> All checks passed
• uv run pytest tests/unit_test/test_format_drift.py -q -> 1 passed
• git diff --check -> clean

Task: #43