feat(provider): 添加独立的 Provider 模块管理模型提供商

实现可扩展的 Provider 系统，支持动态注册自定义提供商：

Core 模块 (packages/core/src/provider/):
- types.ts: Provider 相关类型定义
- builtin/: 内置提供商 (Anthropic, OpenAI, DeepSeek)
- registry.ts: ProviderRegistry 单例类
- config.ts: 配置持久化 (~/.ai-terminal-assistant/providers.json)
- utils.ts: 连接测试等工具函数

Server API (packages/server/src/routes/providers.ts):
- GET/POST/PUT/DELETE /providers 提供商管理
- POST /providers/:id/test 连接测试
- 自定义模型管理接口

Frontend (packages/ui/):
- ProvidersPanel 组件用于管理提供商
- API client 函数和类型定义

主要功能：
- 支持动态注册 OpenAI 兼容服务 (Ollama, vLLM 等)
- 每个提供商独立的 API Key 配置
- 预设模型列表 + 自定义模型输入
- 连接测试验证

packages/ui/src/api/client.ts

@@ -38,6 +38,13 @@ import type {
   SafetyCheckResult,
   UnrevertStatus,
   UnrevertResult,
+  // Provider types
+  ProviderListItem,
+  ProviderDetail,
+  ModelInfo,
+  CustomProviderDefinition,
+  ProviderConfig,
+  ConnectionTestResult,
 } from './types.js';
 
 // Re-export types
@@ -96,6 +103,16 @@ export type {
   CheckpointStats,
   UnrevertStatus,
   UnrevertResult,
+  // Provider types
+  BuiltinProviderType,
+  ProviderType,
+  ModelCapabilities,
+  ModelInfo,
+  ProviderListItem,
+  ProviderDetail,
+  CustomProviderDefinition,
+  ProviderConfig,
+  ConnectionTestResult,
 } from './types.js';
 
 // API Configuration
@@ -804,3 +821,118 @@ export async function getMessageCheckpoints(messageId: string): Promise<{
 }> {
   return request('GET', `/checkpoints/messages/${encodeURIComponent(messageId)}`);
 }
+
+// ============ Providers API ============
+
+/**
+ * 获取所有提供商列表
+ */
+export async function listProviders(): Promise<{
+  success: boolean;
+  data: ProviderListItem[];
+  error?: string;
+}> {
+  return request('GET', '/providers');
+}
+
+/**
+ * 获取单个提供商详情
+ */
+export async function getProvider(id: string): Promise<{
+  success: boolean;
+  data?: ProviderDetail;
+  error?: string;
+}> {
+  return request('GET', `/providers/${encodeURIComponent(id)}`);
+}
+
+/**
+ * 获取提供商的模型列表
+ */
+export async function getProviderModels(id: string): Promise<{
+  success: boolean;
+  data: ModelInfo[];
+  error?: string;
+}> {
+  return request('GET', `/providers/${encodeURIComponent(id)}/models`);
+}
+
+/**
+ * 测试提供商连接
+ */
+export async function testProviderConnection(
+  id: string,
+  apiKey?: string
+): Promise<{
+  success: boolean;
+  data: ConnectionTestResult;
+  error?: string;
+}> {
+  return request('POST', `/providers/${encodeURIComponent(id)}/test`, apiKey ? { apiKey } : {});
+}
+
+/**
+ * 注册自定义提供商
+ */
+export async function registerProvider(
+  definition: CustomProviderDefinition
+): Promise<{
+  success: boolean;
+  message?: string;
+  error?: string;
+}> {
+  return request('POST', '/providers', definition);
+}
+
+/**
+ * 更新提供商配置
+ */
+export async function updateProviderConfig(
+  id: string,
+  config: ProviderConfig
+): Promise<{
+  success: boolean;
+  message?: string;
+  error?: string;
+}> {
+  return request('PUT', `/providers/${encodeURIComponent(id)}`, config);
+}
+
+/**
+ * 删除自定义提供商
+ */
+export async function deleteProvider(id: string): Promise<{
+  success: boolean;
+  message?: string;
+  error?: string;
+}> {
+  return request('DELETE', `/providers/${encodeURIComponent(id)}`);
+}
+
+/**
+ * 添加自定义模型
+ */
+export async function addProviderModel(
+  providerId: string,
+  model: ModelInfo
+): Promise<{
+  success: boolean;
+  message?: string;
+  error?: string;
+}> {
+  return request('POST', `/providers/${encodeURIComponent(providerId)}/models`, model);
+}
+
+/**
+ * 删除自定义模型
+ */
+export async function deleteProviderModel(
+  providerId: string,
+  modelId: string
+): Promise<{
+  success: boolean;
+  message?: string;
+  error?: string;
+}> {
+  return request('DELETE', `/providers/${encodeURIComponent(providerId)}/models/${encodeURIComponent(modelId)}`);
+}