Prune a uv cache after a big install sweep: drop archives with no hardlinks

Installing ~1000 PyPI projects into separate uv venvs grew ~/.cache/uv/archive-v0 to 25 GB (torch-sized wheels), on top of 47 GB of venvs. After deleting the venvs, uv cache prune is not targeted enough. Deleting archive-v0 entries in which no file has a link count above 1 worked: find DIR -type f -links +1 -print -quit comes back empty for those. The remaining venvs kept working, because on this filesystem uv had copied files rather than hardlinked them. Gotcha: some archive dir names start with '-', so use ./ paths or -- with find/rm, or the loop silently skips them.