Add ClaudeMemClient with methods:
- ping(): health check at /api/health
- observe(): fire-and-forget to /api/sessions/observations
- search(): query /api/search with index format
- getObservations(): batch fetch from /api/observations/batch
All methods use AbortSignal.timeout for request timeouts
and handle errors gracefully (worker may be offline).
Part of claude-mem integration (Phase 3/7).
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>