Feature request: Auto-cleanup for stale project entries in .claude.json

Problem

The ~/.claude.json file accumulates project entries indefinitely under the projects key. Each project stores detailed stats (cost, tokens, model usage, session IDs, etc.) that persist forever, even for projects you no longer use.

Currently there are settings like cleanupPeriodDays that clean up chat transcripts, but nothing to prune stale project data.

Proposed Solution

Either:

1. Extend cleanupPeriodDays to also prune project entries that haven't been accessed in X days
2. Add a separate projectCleanupPeriodDays setting for more granular control

Use Case

Users who work on many projects over time end up with a bloated .claude.json file containing historical data for projects they may never revisit.