Fill the package cache for advice

Goal. /just-say-so:advise matches your rejection tags against the rules of every package in the Vale registry, not only the ones installed in the project.

Precondition. Network access to GitHub release pages, about 3 MB.

Steps

Run:
```
/just-say-so:packages --refresh
```
It downloads the 25 writing-rule packages, reads each rule’s id, level, message, and a sample of its tokens, and writes one file per package under packages/ in the state directory. Nothing else downloads an archive, and the archives are never run or written out.
Run /just-say-so:advise. Its first line now reports the cache size and date instead of saying it is empty.

Keeping it fresh

The cache is as old as the last refresh. Advise says so when the oldest package is over 30 days old. /just-say-so:packages alone reports the cache against the registry; --refresh Name refreshes one package; --prune removes packages the registry dropped.