feat(models): auto-mode intent remap + real coder models in preference

Settings "Auto model routing" picks which installed model fires for chat vs
coding intent when no model is pinned (auto_chat_model / auto_code_model).
_auto_select_model honors the remap; _MODEL_PREFERENCE["code"] prefers real
coder models first.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

synapse/memory/store.py

@@ -986,6 +986,10 @@ class PersistentMemoryStore:
     # -----------------------------
     _SETTINGS_DEFAULTS: Dict[str, Any] = {
         "model": "",
+        # Auto-mode routing overrides (blank = built-in preference). When no model
+        # is pinned, a message's detected intent picks which of these fires first.
+        "auto_chat_model": "",
+        "auto_code_model": "",
         # Qwen3-style reasoning. Off by default: the hidden <think> block is pure
         # latency for chat/memory. Turn on for hard multi-step problems.
         "think": False,