feat: add Japanese keyword patterns and session-end auto-save

1. Japanese memory keywords:
   Added patterns like 覚えて, メモして, 保存して, 忘れないで etc.
   so the plugin recognizes Japanese memory trigger phrases.

2. Session-end auto-save:
   - Track user and assistant messages during the session
   - On session.deleted event, ingest the conversation into
     both project and user scopes via supermemory
   - Minimum 3 messages required to trigger save
   - Capped at 50 tracked messages / 50k chars to avoid
     unbounded memory growth