Restore repository-wide Ruff format check for demo generator

[shanev]

Problem

Current main fails uv run ruff format --check . because docs/assets/demo/gen_log.py would be reformatted. The configured CI scope (src tests) remains green, so this regression is not caught after #104 closed.

Acceptance criteria

• docs/assets/demo/gen_log.py is formatted with the repository-pinned Ruff version.
• uv run ruff format --check . passes from a clean checkout.
• Either CI intentionally checks the repository-wide scope or the narrower scope is documented so future non-src Python files do not silently drift.