refactor: 项目结构优化与FastAPI生命周期更新

重构项目目录结构，提高代码组织性和可维护性

将schemas目录重命名为domain，更好地表达领域模型概念
将services目录细分为service/chat、service/image等子目录
将api目录重命名为router，更符合FastAPI惯例
创建utils目录存放通用工具函数
更新FastAPI应用程序生命周期管理

替换已弃用的on_event方法为推荐的lifespan事件处理器
添加应用程序关闭时的日志记录
代码质量改进

抽取常量到constants.py，减少硬编码值
添加helpers.py提供通用工具函数
优化配置管理，使用环境变量和默认值
完善文档字符串，提高代码可读性

app/service/model/model_service.py

@@ -0,0 +1,95 @@
+import requests
+from datetime import datetime, timezone
+from typing import Optional, Dict, Any
+from app.logger.logger import get_model_logger
+from app.config.config import settings
+
+logger = get_model_logger()
+
+class ModelService:
+    def __init__(self, search_models: list, image_models: list):
+        self.search_models = search_models
+        self.image_models = image_models
+        self.base_url = settings.BASE_URL
+        self.filtered_models = settings.FILTERED_MODELS
+
+    def get_gemini_models(self, api_key: str) -> Optional[Dict[str, Any]]:
+        url = f"{self.base_url}/models?key={api_key}"
+
+        try:
+            response = requests.get(url)
+            if response.status_code == 200:
+                gemini_models = response.json()
+                
+                filtered_models_list = []
+                for model in gemini_models.get("models", []):
+                    model_id = model["name"].split("/")[-1]
+                    if model_id not in self.filtered_models:
+                        filtered_models_list.append(model)
+                    else:
+                        logger.info(f"Filtered out model: {model_id}")
+                
+                gemini_models["models"] = filtered_models_list
+                return gemini_models
+            else:
+                logger.error(f"Error: {response.status_code}")
+                logger.error(response.text)
+                return None
+        except requests.RequestException as e:
+            logger.error(f"Request failed: {e}")
+            return None
+
+    def get_gemini_openai_models(self, api_key: str) -> Optional[Dict[str, Any]]:
+        try:
+            gemini_models = self.get_gemini_models(api_key)
+            return self.convert_to_openai_models_format(gemini_models)
+        except requests.RequestException as e:
+            logger.error(f"Request failed: {e}")
+            return None
+
+    def convert_to_openai_models_format(
+            self, gemini_models: Dict[str, Any]
+    ) -> Dict[str, Any]:
+        openai_format = {"object": "list", "data": [], "success": True}
+
+        for model in gemini_models.get("models", []):
+            model_id = model["name"].split("/")[-1]
+            openai_model = {
+                "id": model_id,
+                "object": "model",
+                "created": int(datetime.now(timezone.utc).timestamp()),
+                "owned_by": "google",
+                "permission": [],
+                "root": model["name"],
+                "parent": None,
+            }
+            openai_format["data"].append(openai_model)
+
+            if model_id in self.search_models:
+                search_model = openai_model.copy()
+                search_model["id"] = f"{model_id}-search"
+                openai_format["data"].append(search_model)
+            if model_id in self.image_models:
+                image_model = openai_model.copy()
+                image_model["id"] = f"{model_id}-image"
+                openai_format["data"].append(image_model)
+
+        if settings.CREATE_IMAGE_MODEL:
+            image_model = openai_model.copy()
+            image_model["id"] = f"{settings.CREATE_IMAGE_MODEL}-chat"
+            openai_format["data"].append(image_model)
+        return openai_format
+
+    def check_model_support(self, model: str) -> bool:
+        if not model or not isinstance(model, str):
+            return False
+
+        model = model.strip()
+        if model.endswith("-search"):
+            model = model[:-7]
+            return model in self.search_models
+        if model.endswith("-image"):
+            model = model[:-6]
+            return model in self.image_models
+
+        return model not in self.filtered_models