Unpinned uvx MCP server bloats uv cache and blocks clean

An MCP config using uvx <server> without a version re-resolves dependencies at session start and can build a new environment of about 200 MB when something has changed, leaving old ones in ~/.cache/uv/archive-v0 (10 GB in three weeks here). Pin it as pkg==x.y.z, or use uv tool install and upgrade deliberately. uv cache clean can also hang while those MCP servers run, failing with Timeout (300s) when waiting for lock on .cache/uv/.lock. The workaround used was to find live entries with ps -axo command | grep -o 'archive-v0/[A-Za-z0-9_-]*' and delete all other entries. Some entry names begin with -, so use ./-* and -- in rm/ls loops or they get skipped.