fix(chat): map customer/seller roles for OpenAI-compat LLM; re-contact = mid-chat time-lapse

- llm.complete_conversation now maps internal roles (customer->assistant, seller->user,
  system->system) before the API call — fixes 'Unknown role: customer' (501).
- Re-contact personality: the customer now chats normally, at turn 2 goes quiet and a
  system time-lapse note is shown ('⏳ ผ่านไป 2-3 สัปดาห์...'), then re-engages warmer —
  instead of 'pretending you asked before' at start. Driven by persona.recontact trait.
All 9 backend suites pass. Rebuilt dist.

backend/app/llm.py

@@ -116,12 +116,27 @@ class LLMClient:
         temperature: float = 0.6,
         max_tokens: int = 1200,
     ) -> str:
+        # Normalize internal role labels (customer/seller) to the roles an OpenAI-compatible
+        # chat endpoint accepts: system/user/assistant. customer=assistant (the persona/LLM),
+        # seller=user (the trainee). Anything else maps to a safe default.
+        api_messages = []
+        for m in messages:
+            role = (m.get("role") or "").lower()
+            if role == "system":
+                mapped = "system"
+            elif role in ("customer", "assistant"):
+                mapped = "assistant"
+            elif role in ("seller", "user"):
+                mapped = "user"
+            else:
+                mapped = "user"
+            api_messages.append({"role": mapped, "content": m.get("text") or m.get("content") or ""})
         try:
             resp = self.client.chat.completions.create(
                 model=self.model,
                 temperature=temperature,
                 max_tokens=max_tokens,
-                messages=messages,
+                messages=api_messages,
             )
         except Exception as exc:
             raise LLMError(f"LLM call failed: {exc}") from exc