fix(scenario): recontact chats normally first then re-engages mid-chat; channel default=social; remove 'add more' button (15 personas auto)

- recontact persona now opens as a NORMAL customer (no 'I asked before' in the opening);
  the mid-chat time-lapse system note (turn 2) makes them re-engage warmer instead.
- channel default changed facebook->social everywhere (create/analyze/store/simulator/me).
- 15 personas auto-generated (TARGET=15); removed the 'สร้างบุคคลต้นแบบเพิ่มเติม' button/guide.
All 9 backend suites pass. Rebuilt dist.

backend/app/services/own_persona.py

@@ -35,7 +35,7 @@ def generate_own_persona(llm: LLMClient, *, mode: str, spec: dict[str, Any]) ->
     if not isinstance(persona, dict):
         raise ValueError("own-persona generator returned invalid data")
     persona.setdefault("tier", "B")
-    persona.setdefault("channel", "facebook")
+    persona.setdefault("channel", "social")
     persona.setdefault("initiation_mode", "customer")
     persona.setdefault("pains", [])
     persona.setdefault("negotiation_levers", [])