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/key/key_manager.py

@@ -0,0 +1,105 @@
+import asyncio
+from itertools import cycle
+from typing import Dict
+from app.logger.logger import get_key_manager_logger
+from app.config.config import settings
+
+
+logger = get_key_manager_logger()
+
+
+class KeyManager:
+    def __init__(self, api_keys: list):
+        self.api_keys = api_keys
+        self.key_cycle = cycle(api_keys)
+        self.key_cycle_lock = asyncio.Lock()
+        self.failure_count_lock = asyncio.Lock()
+        self.key_failure_counts: Dict[str, int] = {key: 0 for key in api_keys}
+        self.MAX_FAILURES = settings.MAX_FAILURES
+        self.paid_key = settings.PAID_KEY
+
+    async def get_paid_key(self) -> str:
+        return self.paid_key
+        
+    async def get_next_key(self) -> str:
+        """获取下一个API key"""
+        async with self.key_cycle_lock:
+            return next(self.key_cycle)
+
+    async def is_key_valid(self, key: str) -> bool:
+        """检查key是否有效"""
+        async with self.failure_count_lock:
+            return self.key_failure_counts[key] < self.MAX_FAILURES
+
+    async def reset_failure_counts(self):
+        """重置所有key的失败计数"""
+        async with self.failure_count_lock:
+            for key in self.key_failure_counts:
+                self.key_failure_counts[key] = 0
+
+    async def get_next_working_key(self) -> str:
+        """获取下一可用的API key"""
+        initial_key = await self.get_next_key()
+        current_key = initial_key
+
+        while True:
+            if await self.is_key_valid(current_key):
+                return current_key
+
+            current_key = await self.get_next_key()
+            if current_key == initial_key:
+                # await self.reset_failure_counts() 取消重置
+                return current_key
+
+    async def handle_api_failure(self, api_key: str) -> str:
+        """处理API调用失败"""
+        async with self.failure_count_lock:
+            self.key_failure_counts[api_key] += 1
+            if self.key_failure_counts[api_key] >= self.MAX_FAILURES:
+                logger.warning(
+                    f"API key {api_key} has failed {self.MAX_FAILURES} times"
+                )
+
+        return await self.get_next_working_key()
+
+    def get_fail_count(self, key: str) -> int:
+        """获取指定密钥的失败次数"""
+        return self.key_failure_counts.get(key, 0)
+
+    async def get_keys_by_status(self) -> dict:
+        """获取分类后的API key列表，包括失败次数"""
+        valid_keys = {}
+        invalid_keys = {}
+        
+        async with self.failure_count_lock:
+            for key in self.api_keys:
+                fail_count = self.key_failure_counts[key]
+                if fail_count < self.MAX_FAILURES:
+                    valid_keys[key] = fail_count
+                else:
+                    invalid_keys[key] = fail_count
+        
+        return {
+            "valid_keys": valid_keys,
+            "invalid_keys": invalid_keys
+        }
+        
+        
+_singleton_instance = None
+_singleton_lock = asyncio.Lock()
+
+async def get_key_manager_instance(api_keys: list = None) -> KeyManager:
+    """
+    获取 KeyManager 单例实例。
+
+    如果尚未创建实例，将使用提供的 api_keys 初始化 KeyManager。
+    如果已创建实例，则忽略 api_keys 参数，返回现有单例。
+    """
+    global _singleton_instance
+
+    async with _singleton_lock:
+        if _singleton_instance is None:
+            if api_keys is None:
+                raise ValueError("API keys are required to initialize the KeyManager")
+            _singleton_instance = KeyManager(api_keys)
+        return _singleton_instance