chore: 完善开源项目文档与结构，移除敏感原始图片

- 重写 README.md，添加在线体验、API 文档、部署指南、技术栈等
- 添加 MIT LICENSE
- 添加 CONTRIBUTING.md 贡献指南
- 添加 GitHub Issue/PR 模板
- 完善 .gitignore，防止原始图片和敏感文件误提交
- 从 git 中移除 25 个原始图片文件（.png/.jpg/非序号 webp）
- 项目结构迁移：functions/ -> src/，根目录静态文件 -> public/
- 添加 wrangler.toml 与 package.json 配置

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 shumengya
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.