feat: conversation long-term memory + fix source ENUM bug
- New: conversationSummarizer.js (LLM summary every 3 turns, loadBestSummary, persistFinalSummary)
- db/index.js: conversation_summaries table, upsertConversationSummary, getSessionSummary
- redisClient.js: setSummary/getSummary (TTL 2h)
- nativeVoiceGateway.js: _turnCount tracking, trigger summarize, persist on close
- realtimeDialogRouting.js: inject summary context, reduce history 5->3 rounds
- Fix: messages source ENUM missing 'search_knowledge' causing chat DB writes to fail
fe25229de7