实现 AI Core 与 Agent Core 基础功能

- 更新 README 描述从后端壳子到 AI Core/Agent Core
- 添加 ToolCall 和 ToolResult 数据结构定义
- 扩展 AgentRun 模型增加输出、错误码、工具调用结果等字段
- 添加 mock 提供商类型支持
- 实现聊天、代理运行、工具调用和提供商管理的核心路由逻辑
- 集成容器化依赖注入和错误处理机制
- 更新 API 接口契约和文档说明

backend/app/providers/registry.py

@@ -0,0 +1,55 @@
+from dataclasses import dataclass
+from time import perf_counter
+
+from app.contracts import ModelInfo, ProviderConfig, ProviderTestResponse
+from app.providers.base import ModelProvider
+
+
+class ProviderNotFoundError(LookupError):
+    pass
+
+
+@dataclass(slots=True)
+class RegisteredProvider:
+    config: ProviderConfig
+    adapter: ModelProvider
+
+
+class ProviderRegistry:
+    def __init__(self) -> None:
+        self._providers: dict[str, RegisteredProvider] = {}
+
+    def register(self, config: ProviderConfig, adapter: ModelProvider) -> None:
+        if config.provider_id in self._providers:
+            raise ValueError(f"Provider already registered: {config.provider_id}")
+        self._providers[config.provider_id] = RegisteredProvider(config=config, adapter=adapter)
+
+    def unregister(self, provider_id: str) -> None:
+        self._providers.pop(provider_id, None)
+
+    def get(self, provider_id: str) -> RegisteredProvider:
+        try:
+            provider = self._providers[provider_id]
+        except KeyError as exc:
+            raise ProviderNotFoundError(provider_id) from exc
+        if not provider.config.enabled:
+            raise ProviderNotFoundError(provider_id)
+        return provider
+
+    def list_configs(self) -> list[ProviderConfig]:
+        return [item.config.model_copy(deep=True) for item in self._providers.values()]
+
+    async def list_models(self, provider_id: str) -> list[ModelInfo]:
+        return await self.get(provider_id).adapter.list_models()
+
+    async def test(self, provider_id: str, model: str | None = None) -> ProviderTestResponse:
+        provider = self.get(provider_id)
+        started = perf_counter()
+        success, message = await provider.adapter.test_connection(model)
+        latency_ms = round((perf_counter() - started) * 1000)
+        return ProviderTestResponse(
+            provider_id=provider_id,
+            success=success,
+            latency_ms=latency_ms,
+            message=message,
+        )