timestamper-python: Refactor, CLI and CI

Split a single-file YouTube chapter generator into modules, added CLI options, and set up lint, format and type-check workflows.

timestamper-python generates YouTube chapter timestamps from captions, using OpenAI to title each chapter. All the logic lived in one script.

  • Refactor and CLI (#1): split the code into captions, chapters, titles, utils and cli modules, added type hints and logging, and added command-line arguments for settings like the caption language. Behavior stayed the same.
  • CI (#2): added GitHub Actions workflows for ruff, black --check and mypy on every push and PR.

Links: PR #1 • PR #2