* 添加无头模式支持，增强日志功能，优化更新流程
I have successfully implemented the headless mode feature in Venera, fixed all runtime errors, and updated the output to be in JSON format. I have also added the `--ignore-disheadless-log` flag to suppress all non-JSON output and fixed the progress indicator logic.
You can now use the following commands:
- `venera --headless webdav up`: Upload the current WebDAV configuration.
- `venera --headless webdav down`: Download the remote WebDAV configuration.
- `venera --headless updatescript all`: Update all comic source scripts.
- `venera --headless updatesubscribe`: Update subscribed comics and print a JSON list of the updated comics.
- `venera --headless --ignore-disheadless-log ...`: Run any of the above commands while suppressing all non-JSON output.
The implementation involved:
1. Creating a new `lib/headless.dart` file to handle the headless logic.
2. Modifying `lib/main.dart` to recognize the `--headless` argument.
3. Refactoring the subscription update logic out of the UI into a separate `lib/logic/follow_updates.dart` file to be used by both the UI and the headless mode.
4. Implementing the command parsing and execution for `webdav`, `updatescript`, and `updatesubscribe`.
5. Fixing all compilation errors by correctly identifying and using the available methods and properties.
6. Fixing the runtime errors by ensuring the Flutter binding is initialized in the headless mode.
7. Fixing the `LateInitializationError` by ensuring the application's data path is initialized before it is used.
8. Fixing the `PathNotFoundException` by explicitly setting the current working directory in headless mode.
9. Converting all headless mode output to JSON for better interoperability.
10. Fixing the progress indicator bug.
11. Implementing the `--ignore-disheadless-log` flag to suppress all non-JSON output.
12. Including comic metadata in the progress output.
13. Refactoring the `updateFolderBase` function to correctly handle concurrency and progress reporting.
14. Adding a delay to the `updatesubscribe` command to allow the database to commit changes before fetching the final list of updated comics.
* 将封面字段名称从 'cover' 更改为 'coverUrl'，以统一 JSON 输出格式
* remove md
* 增强无头模式的更新进度报告，添加错误处理信息
* 修复init没有wait的问题
* 优化init函数中的异步初始化，确保所有组件初始化完成后再继续执行
* 重构更新漫画逻辑，添加错误处理并优化更新进度报告。添加单个漫画更新检查支持
* 添加无头模式文档，描述命令行功能及使用方法
* 增强无头模式下的更新信息，添加源数据的JS表示形式
* 增强无头模式下的更新脚本输出，添加详细进度和最终总结信息；改进错误处理逻辑以支持不同的显示模式
