feat(chat): 新增聊天记录离线导出接口

- 支持批量范围（选中/全部/群聊/单聊）与时间筛选
- 支持 json/txt 导出并打包为 zip，附带 manifest/report
- 可选打包离线媒体与头像；隐私模式下隐藏字段并禁用媒体/头像
- 提供任务查询/取消/下载与 SSE 进度事件流
- 修复导出路径名清理的正则误伤

src/wechat_decrypt_tool/api.py

@@ -6,6 +6,7 @@ from fastapi.middleware.cors import CORSMiddleware
 from .logging_config import setup_logging, get_logger
 from .path_fix import PathFixRoute
 from .routers.chat import router as _chat_router
+from .routers.chat_export import router as _chat_export_router
 from .routers.chat_media import router as _chat_media_router
 from .routers.decrypt import router as _decrypt_router
 from .routers.health import router as _health_router
@@ -39,6 +40,7 @@ app.include_router(_wechat_detection_router)
 app.include_router(_decrypt_router)
 app.include_router(_media_router)
 app.include_router(_chat_router)
+app.include_router(_chat_export_router)
 app.include_router(_chat_media_router)