Enhance credential management and testing functionality

- Introduce new fields for voice, speed, and language in the AssistantConfig and ProviderCredential models to support TTS and ASR configurations.
- Update the database schema and seeding script to accommodate the new fields, ensuring backward compatibility.
- Implement credential testing endpoints and logic to validate OpenAI-compatible credentials, enhancing user experience and reliability.
- Modify frontend components to include new fields in the credential forms and improve connection testing feedback.
- Refactor related services and API interactions to support the new credential testing feature.

backend/db/models.py

@@ -9,7 +9,7 @@
 
 from datetime import datetime
 
-from sqlalchemy import JSON, Boolean, DateTime, ForeignKey, String, func
+from sqlalchemy import JSON, Boolean, DateTime, Float, ForeignKey, String, func
 from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
 
 
@@ -29,6 +29,9 @@ class ProviderCredential(Base):
     interface_type: Mapped[str] = mapped_column(String(32), default="openai")  # openai|xfyun|dashscope|gemini
     api_url: Mapped[str] = mapped_column(String(512), default="")
     api_key: Mapped[str] = mapped_column(String(512), default="")   # 明文
+    voice: Mapped[str] = mapped_column(String(128), default="")     # TTS 音色
+    speed: Mapped[float] = mapped_column(Float, default=1.0)        # TTS 语速
+    language: Mapped[str] = mapped_column(String(32), default="")   # ASR 语言
     # 同一 type 下的默认凭证(后端解析用;前端 ModelResource 无此字段,留作可选)
     is_default: Mapped[bool] = mapped_column(Boolean, default=False)
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())