Add --update self-update command

Added

• xpilot --update self-update command: checks the project's GitHub Release for a newer version and installs it automatically — preferring the wheel attached to the release, then the sdist tarball, falling back to building from the tagged source when neither is present; reports and exits when already on the latest version. xpilot is distributed only via GitHub Release (not published on PyPI), so the update source points to GitHub Release rather than pip install --upgrade xpilot. Adds the xpilot/updater.py module (latest-release lookup, version comparison, asset selection, pip install) with tests/test_updater.py unit tests.

Changed

• Fixed a version baseline mismatch: xpilot/__init__.py __version__ and the cli.py --version output were synced from 0.1.0 to 0.1.1 to align with VERSION, so --update compares against an accurate current version.

Full Changelog: v0.1.1...v0.2.0