feat: 添加LLM配置持久化功能 [AC-AISVC-50]

- LLM配置保存到 config/llm_config.json 文件
- 服务重启后自动加载已保存的配置
- 与嵌入模型配置保持一致的持久化机制

ai-service/app/services/llm/factory.py

@@ -5,8 +5,10 @@ LLM Provider Factory and Configuration Management.
 Design pattern: Factory pattern for pluggable LLM providers.
 """
 
+import json
 import logging
 from dataclasses import dataclass, field
+from pathlib import Path
 from typing import Any
 
 from app.services.llm.base import LLMClient, LLMConfig
@@ -14,6 +16,8 @@ from app.services.llm.openai_client import OpenAIClient
 
 logger = logging.getLogger(__name__)
 
+LLM_CONFIG_FILE = Path("config/llm_config.json")
+
 
 @dataclass
 class LLMProviderInfo:
@@ -257,7 +261,7 @@ class LLMProviderFactory:
 class LLMConfigManager:
     """
     Manager for LLM configuration.
-    [AC-ASA-16, AC-ASA-17, AC-ASA-18] Configuration management with hot-reload.
+    [AC-ASA-16, AC-ASA-17, AC-ASA-18] Configuration management with hot-reload and persistence.
     """
 
     def __init__(self):
@@ -274,12 +278,41 @@ class LLMConfigManager:
             "temperature": settings.llm_temperature,
         }
         self._client: LLMClient | None = None
+        
+        self._load_from_file()
+
+    def _load_from_file(self) -> None:
+        """Load configuration from file if exists."""
+        try:
+            if LLM_CONFIG_FILE.exists():
+                with open(LLM_CONFIG_FILE, 'r', encoding='utf-8') as f:
+                    saved = json.load(f)
+                    self._current_provider = saved.get("provider", self._current_provider)
+                    saved_config = saved.get("config", {})
+                    if saved_config:
+                        self._current_config.update(saved_config)
+                    logger.info(f"[AC-ASA-16] Loaded LLM config from file: provider={self._current_provider}")
+        except Exception as e:
+            logger.warning(f"[AC-ASA-16] Failed to load LLM config from file: {e}")
+
+    def _save_to_file(self) -> None:
+        """Save configuration to file."""
+        try:
+            LLM_CONFIG_FILE.parent.mkdir(parents=True, exist_ok=True)
+            with open(LLM_CONFIG_FILE, 'w', encoding='utf-8') as f:
+                json.dump({
+                    "provider": self._current_provider,
+                    "config": self._current_config,
+                }, f, indent=2, ensure_ascii=False)
+            logger.info(f"[AC-ASA-16] Saved LLM config to file: provider={self._current_provider}")
+        except Exception as e:
+            logger.error(f"[AC-ASA-16] Failed to save LLM config to file: {e}")
 
     def get_current_config(self) -> dict[str, Any]:
         """Get current LLM configuration."""
         return {
             "provider": self._current_provider,
-            "config": self._current_config,
+            "config": self._current_config.copy(),
         }
 
     async def update_config(
@@ -289,7 +322,7 @@ class LLMConfigManager:
     ) -> bool:
         """
         Update LLM configuration.
-        [AC-ASA-16] Hot-reload configuration.
+        [AC-ASA-16] Hot-reload configuration with persistence.
 
         Args:
             provider: Provider name
@@ -310,6 +343,8 @@ class LLMConfigManager:
 
         self._current_provider = provider
         self._current_config = validated_config
+        
+        self._save_to_file()
 
         logger.info(f"[AC-ASA-16] LLM config updated: provider={provider}")
         return True
@@ -365,7 +400,7 @@ class LLMConfigManager:
         test_provider = provider or self._current_provider
         test_config = config if config else self._current_config
         
-        logger.info(f"[AC-ASA-17] Test connection: provider={test_provider}, config={test_config}")
+        logger.info(f"[AC-ASA-17] Test connection: provider={test_provider}, model={test_config.get('model')}")
 
         if test_provider not in LLM_PROVIDERS:
             return {