- Create snapshotter package with periodic (10 min) and on-demand snapshots
- Add JSON serialization with gzip compression and atomic file writes
- Update routing table to track AddedAt time for each route
- Load snapshots on startup, filtering out stale routes (>30 minutes old)
- Add ROUTEWATCH_DISABLE_SNAPSHOTTER env var for tests
- Use OS-appropriate state directories (macOS: ~/Library/Application Support, Linux: /var/lib or XDG_STATE_HOME)