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

honcho_integration/__init__.py

@@ -0,0 +1,9 @@
+"""Honcho integration for AI-native memory.
+
+This package is only active when honcho.enabled=true in config and
+HONCHO_API_KEY is set. All honcho-ai imports are deferred to avoid
+ImportError when the package is not installed.
+
+Named ``honcho_integration`` (not ``honcho``) to avoid shadowing the
+``honcho`` package installed by the ``honcho-ai`` SDK.
+"""