adds uv to the list of package managers pull auto-installs, so python projects using uv get synced after a fetch like the js/ruby/php ones already do.

• runs uv sync when uv.lock or pyproject.toml changes on pull
• anchored on uv.lock existing so it never fires against a non-uv pyproject.toml (poetry/hatch/pip-tools all use one too)
• opt out with GIT_FRIENDLY_NO_UV=true, documented in the readme

to test:

• in a uv repo, pull a commit that touches uv.lock → should print "Installing packages with uv..." and run uv sync
• in a pyproject-only repo with no uv.lock, pull → uv should not run