refactor(scenario): only 2 scenarios (social / face-to-face); 're-contact' becomes a persona trait

- Scenario picker now has only social + f2f_call (removed recontact) in backend
  _scenarios, start_session validation, and Chat.vue picker.
- 'ลูกค้ากลับมาติดต่อ' is no longer a scenario: it's now a PERSONA trait. Persona prompt
  generates ~1-in-4 personas with recontact=true (asked before, now returns warmer/ready);
  store shape gets recontact field; simulator injects a re-contact note into the persona's
  system prompt so it plays as a returning customer naturally.
- test_scenario updated: unknown scenario defaults to social; recontact shown as a
  generated persona trait.
All 9 backend suites pass. Rebuilt dist.

backend/app/services/store.py

@@ -43,6 +43,7 @@ def ensure_persona_shape(p: dict[str, Any]) -> dict[str, Any]:
         "negotiation_levers": p.get("negotiation_levers", []),
         "opener": p.get("opener", ""),
         "special": p.get("special", ""),       # e.g. "wrong_text" | ""
+        "recontact": bool(p.get("recontact")),  # returned after researching earlier (pre-qualified, warm)
         "difficulty": p.get("difficulty", 1),  # 1..5
         "tolerance": p.get("tolerance", 3),    # misses before this persona walks away (temper)
         "notes": p.get("notes", ""),