fix: 3 fixes for Step 2, Step 4, Step 5

1. Step 5: Use empty model_config_dict={} so camel-ai doesn't spread
   api_key into create() - AsyncOpenAI reads env vars automatically.
   Step 3 unaffected (same env vars, just cleaner ModelFactory call).

2. Step 2: Fix Thai text truncation - isalnum() stripped Thai chars.
   Use re.sub(r'[^\w]', '', username, re.UNICODE) instead.

3. Step 4: Move get_language_instruction() to START of prompt (not end)
   and strengthen wording with MUST/IMPORTANT prefix.

backend/app/services/oasis_profile_generator.py

@@ -274,12 +274,14 @@ class OasisProfileGenerator:
         )
     
     def _generate_username(self, name: str) -> str:
-        """生成用户名"""
-        # 移除特殊字符，转换为小写
+        """Generate a username from the entity name"""
+        # Keep Unicode characters (Thai, Chinese, etc) and convert to lowercase
         username = name.lower().replace(" ", "_")
-        username = ''.join(c for c in username if c.isalnum() or c == '_')
+        # Only remove truly problematic characters for usernames
+        import re
+        username = re.sub(r'[^\w]', '', username, flags=re.UNICODE)
         
-        # 添加随机后缀避免重复
+        # Add random suffix to avoid duplicates
         suffix = random.randint(100, 999)
         return f"{username}_{suffix}"