新增文件上传限制配置，支持导出Markdown文件为ZIP格式；更新相关文档和API处理逻辑

[239573049]

This pull request introduces functionality to export warehouse documents as a Markdown ZIP file and sets a configurable maximum file upload size. The changes span backend, frontend, and documentation updates to support these features.

Backend Changes:

• Added Markdown Export Logic:

  • Implemented the ExportMarkdownZip method in WarehouseService to generate and return a ZIP file containing Markdown files for all documents in a warehouse. This includes recursive handling of document catalogs. (src/KoalaWiki/Services/WarehouseService.cs, src/KoalaWiki/Services/WarehouseService.csR391-R495)

• Introduced MaxFileLimit Configuration:

  • Added a MaxFileLimit property to OpenAIOptions and updated the InitConfig method to read its value from configuration. (src/KoalaWiki/Options/OpenAIOptions.cs, [1] [2]
  • Configured file upload size limits in Program.cs using the MaxFileLimit value. (src/KoalaWiki/Program.cs, src/KoalaWiki/Program.csR28-R37)

Frontend Changes:

• Export Markdown Button:

  • Added a button in the repository layout (layout.client.tsx) to trigger the Markdown export feature. The button uses a modal for confirmation and downloads the ZIP file upon success. (web/app/[owner]/[name]/layout.client.tsx, web/app/[owner]/[name]/layout.client.tsxL532-R624, web/app/[owner]/[name]/layout.client.tsxL762-R831)

• Client API Updates:

  • Updated clientFetchApi to handle ZIP file responses and added a new ExportMarkdownZip service for triggering the export API. (web/app/services/api.ts, [1]; web/app/services/warehouseService.ts, [2]

Documentation Updates:

• Configurable Options:

  • Documented the new MAX_FILE_LIMIT configuration in both English (README.md) and Chinese (README.zh-CN.md). [1] [2]

• Graph Representation:

  • Updated the graph TD sections in both documentation files to include MAX_FILE_LIMIT. [1] [2]