feat: verbose make targets, separate bump from release, tag-triggered publish

[smorin]

Summary

• Verbose make targets: Removed @ prefix from convenience targets (version, bump-patch, bump-minor, bump-major, release) so they print the underlying commands, teaching users what's happening
• Separate bump from release: make release no longer bumps — run make bump-patch/minor/major first, then make release to sync/commit/tag
• Tag-triggered publish: Changed CI from release:published to push:tags:v* so pushing a tag automatically publishes to PyPI
• Auto GitHub Release: Added a release job that creates a GitHub Release with auto-generated notes after PyPI publish
• Updated docs: RELEASE.md and README.md reflect the new streamlined workflow

Example output with verbose targets:

$ make bump-patch
uv run python scripts/bump_version.py patch
0.3.1 -> 0.3.2

$ make version
uv run python -c "from importlib.metadata import version; print(version('worktreeflow'))"
0.3.2

Test plan

• All 159 tests pass (make test)
• make version prints command then version
• make bump-patch --dry-run shows uv run python scripts/bump_version.py patch
• End-to-end: make bump-patch && make release && git push --tags triggers CI publish