fix(persona): natural Thai openers - 'สวัสดีครับ/ค่ะ' + direct question, no 'เฮ้/เอ้'

- persona_prompts OPENER RULE: mandate polite Thai openers that start
  with สวัสดีครับ/ค่ะ and go straight to the question or 'สนใจ/สอบถาม';
  explicitly forbid casual English fillers (เฮ้/เอ้/เอ่อ/hey) and
  singsong slang for Thai
- chat_routes: default opener fallback is now locale-aware - Thai locale
  uses 'สวัสดีครับ สนใจสินค้าของคุณครับ...' instead of the English one

backend/app/api/chat_routes.py

@@ -327,7 +327,7 @@ def start_session(gid: str, pid: str):
     if scenario_meta.get("preamble"):
         seeded.append({"role": "system", "text": scenario_meta["preamble"]})
     if init_mode == "customer":
-        opener = persona.get("opener") or "Hi, I saw your product and had a question."
+        opener = persona.get("opener") or (("สวัสดีครับ สนใจสินค้าของคุณครับ ขอถามรายละเอียดหน่อยได้ไหม" if locale == "th" else "Hi, I saw your product and had a question."))
         seeded.append({"role": "customer", "text": opener})
     initial_internal = {"turns": 0, "score": 50, "signals": []}
 
@@ -348,7 +348,7 @@ def start_session(gid: str, pid: str):
             if scenario_meta.get("preamble"):
                 seeded.append({"role": "system", "text": scenario_meta["preamble"]})
             if init_mode == "customer":
-                opener = persona.get("opener") or "Hi, I saw your product and had a question."
+                opener = persona.get("opener") or (("สวัสดีครับ สนใจสินค้าของคุณครับ ขอถามรายละเอียดหน่อยได้ไหม" if locale == "th" else "Hi, I saw your product and had a question."))
                 seeded.append({"role": "customer", "text": opener})
             session, resumed = s["sessions"].start(
                 org_id=org_id,

backend/app/services/persona_prompts.py

@@ -50,11 +50,14 @@ RULES:
 7. difficulty 1-5. special="" unless wrong_text.
 8. OPENER RULE (IMPORTANT): the `opener` is what the customer says FIRST when initiation_mode="customer".
    Every opener — for EVERY tier, including wrong_text and every tier-C persona — must be a natural, polite,
-   in-character customer greeting that starts warmly or neutrally and expresses some interest or a question
-   (e.g. "สวัสดีค่ะ เห็นสินค้าคุณแล้ว สนใจอยากสอบถาม" / "สวัสดีครับ เข้าไปดูเพจมา อยากถามราคาหน่อย" / "Hi, I saw
-   your page and had a question"). NEVER make the opener a complaint, a refusal, a price grumble, a "never
-   mind", or anything negative — the customer's resistance must only surface DURING the conversation, not
-   in their very first message.
+   in-character customer greeting that starts warmly or neutrally and expresses some interest or a question.
+   EXAMPLES (Thai): "สวัสดีครับ สนใจสินค้าตัวนี้ ขอถามราคาหน่อยได้ไหม" / "สวัสดีค่ะ เห็นโฆษณาแฟนเพจมา เลยอยากสอบถาม" / "สวัสดีครับ ซื้อของที่นี่แล้วสั่ง-จัดส่งยังไงบ้าง" / "สนใจสินค้าในแฟนเพจครับ สอบถามรายละเอียดได้ไหม".
+   THAI STYLE (MANDATORY): Start with "สวัสดีครับ/ค่ะ" then go straight to the question or the word "สนใจ/สอบถาม" —
+   do NOT open with casual English-style interjections or filler like "เฮ้", "เอ้", "เอ่อ", "hey", "hi ya", or
+   singsong slang ("ไง", "นี่ๆ", "ว่าไง"). A question that gets to the point directly is ideal. For English,
+   a plain "Hi" or "Hello" is fine.
+   NEVER make the opener a complaint, a refusal, a price grumble, a "never mind", or anything negative — the
+   customer's resistance must only surface DURING the conversation, not in their very first message.
 9. Language: output all human text in the requested language.
 Only output valid JSON: {"personas": [ ... ]}
 """