refactor: 创建 @anthropic-ai/model-provider 包骨架与类型定义

- 新建 workspace 包 packages/@anthropic-ai/model-provider
- 定义 ModelProviderHooks 接口（依赖注入：分析、成本、日志等）
- 定义 ClientFactories 接口（Anthropic/OpenAI/Gemini/Grok 客户端工厂）
- 搬入核心类型：Message 体系、NonNullableUsage、EMPTY_USAGE、SystemPrompt、错误常量
- 主项目 src/types/message.ts 等改为 re-export，保持向后兼容

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -31,7 +31,8 @@
   },
   "workspaces": [
     "packages/*",
-    "packages/@ant/*"
+    "packages/@ant/*",
+    "packages/@anthropic-ai/*"
   ],
   "files": [
     "dist",
@@ -63,6 +64,7 @@
     "@langfuse/tracing": "^5.1.0",
     "@types/lodash-es": "^4.17.12",
     "@alcalzone/ansi-tokenize": "^0.3.0",
+    "@anthropic-ai/model-provider": "workspace:*",
     "@ant/claude-for-chrome-mcp": "workspace:*",
     "@ant/computer-use-input": "workspace:*",
     "@ant/computer-use-mcp": "workspace:*",