refactor: vendor marked + dompurify 到项目内，实现零外部依赖

- marked (77行 ESM) + dompurify (1398行 ESM) 复制到 src/vendor/
- 包含 LICENSE 文件和类型声明（dompurify 类型去除 trusted-types 外部依赖）
- 移除 package.json 中 marked/dompurify/@types/dompurify 依赖
- 移除 electron-builder files 配置中的 node_modules 引用
- tsconfig.json include 新增 src/vendor/**/*.d.ts

tsconfig.json

@@ -18,6 +18,6 @@
     "rootDir": "src/renderer",
     "lib": ["ES2022", "DOM", "DOM.Iterable"]
   },
-  "include": ["src/renderer/**/*.ts", "src/renderer/**/*.d.ts"],
+  "include": ["src/renderer/**/*.ts", "src/renderer/**/*.d.ts", "src/vendor/**/*.d.ts"],
   "exclude": ["node_modules", "dist", "release"]
 }