v0.1.0

Prepare mobbo-serial for PyPI publishing

- Add MIT LICENSE and complete PyPI-facing metadata in pyproject.toml
  (description, authors, classifiers, keywords, project URLs)
- Move PySide6 to an optional [gui] extra - the mobbo package itself
  never imports Qt, only the sample_gui.py demo does, so it shouldn't
  be a hard dependency for library consumers
- Add .github/workflows/ci.yml: run pytest on push/PR across
  ubuntu/windows/macos
- Add .github/workflows/publish.yml: build and publish to PyPI via
  Trusted Publishing (OIDC) when a GitHub Release is published - no
  API token stored in the repo
- Update README with install/[gui] extra/release instructions

Verified: package builds correctly (wheel only contains mobbo/, not
sample_gui.py/tests/docs), metadata renders correctly, 39/39 tests
still pass.