Feature request: plugin cache garbage collection (claude plugin gc)

Problem

The plugin cache at ~/.claude/plugins/cache/ accumulates stale artifacts over time with no cleanup mechanism:

1. Orphaned plugin versions — When claude plugin update installs a new version, it drops a .orphaned_at marker in the old version directory but never deletes it. Over multiple updates, these accumulate.

1. Temp clone directories — temp_git_* directories are created during plugin add / plugin update git clone operations but are never cleaned up. In my setup, 35 of these accumulated totaling ~50MB.

1. Disabled plugin caches — Disabled plugins retain their full cache. No option to reclaim space.

Current state (real example)

Orphaned versions:     7 directories (~1.6MB)
Temp git artifacts:   35 directories (~50MB)
Active plugin cache:  16 versions

Proposed solution

claude plugin gc

$ claude plugin gc
Scanning plugin cache...

Orphaned versions:     7 (1.6 MB)
Temp clone artifacts: 35 (50.2 MB)
Total reclaimable:    51.8 MB

Remove all? [y/N]

Options:

• --dry-run — show what would be removed
• --force — skip confirmation
• --keep-last N — retain N previous versions for rollback (default: 0)

Auto-cleanup on update

When claude plugin update succeeds, automatically remove the previous version's cache directory (or at least the temp_git_* used for the clone).

Bulk update

Also useful: claude plugin update --all to update all installed plugins in one command, rather than requiring per-plugin invocations.