feat: add Honcho AI-native memory integration

Opt-in persistent cross-session user modeling via Honcho. Reads
~/.honcho/config.json as single source of truth (shared with
Claude Code, Cursor, and other Honcho-enabled tools). Zero impact
when disabled or unconfigured.

- honcho_integration/ package (client, session manager, peer resolution)
- Host-based config resolution matching claude-honcho/cursor-honcho pattern
- Prefetch user context into system prompt per conversation turn
- Sync user/assistant messages to Honcho after each exchange
- query_user_context tool for mid-conversation dialectic reasoning
- Gated activation: requires ~/.honcho/config.json with enabled=true

model_tools.py

@@ -93,6 +93,7 @@ def _discover_tools():
         "tools.delegate_tool",
         "tools.process_registry",
         "tools.send_message_tool",
+        "tools.honcho_tools",
     ]
     import importlib
     for mod_name in _modules: