feat: Expose new MCP tools as HTTP API endpoints

Adds 10 new REST endpoints matching recently added MCP tools:

Progressive Disclosure:
- GET  /api/memories/search-index  (compact token-efficient search)
- GET  /api/memories/timeline      (chronological navigation around anchor)
- POST /api/memories/fetch         (batch fetch full details by IDs)

Goal Management:
- POST /api/goals                  (set/update a goal)
- GET  /api/goals                  (list active goals)
- POST /api/goals/{key}/complete   (mark goal complete)

Summarization (requires LLM):
- POST /api/summarize/session      (summarize session memories)
- POST /api/summarize/context      (summarize recent context)

Auto-Capture:
- GET  /api/captures/status        (check capture buffer status)
- POST /api/captures/drain         (drain JSONL entries into memories)

https://claude.ai/code/session_01M5GUmiM8WehUBUvKWiWgcJ

Author: claude