Provision and reuse a global uv environment for ad hoc Python scripts.
- Replaced the install script reference from `uv-global.sh` to `install.sh`; removed the old script and added the new one. - Installation instructions updated to mention new shims added to `~/.uv-global/.venv/bin`. - Clarified that the PATH update makes both the global environment and shims available. - General documentation enhancements for clarity.