docs(ai): 添加 RAGFlow MCP 部署文档与 AI 栏目整理

- 新增 Windows 11 RAGFlow + MCP 完整部署记录
- 添加 AI 栏目首页与免费模型 API 文档
- 更新 VuePress 配置与 collections 结构
- 添加缓存清理和文档同步脚本

scripts/clear-vuepress-cache.mjs

@@ -0,0 +1,12 @@
+import { rmSync, existsSync } from 'node:fs'
+import { join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const root = join(fileURLToPath(new URL('.', import.meta.url)), '..')
+const cache = join(root, 'docs', '.vuepress', '.cache')
+if (existsSync(cache)) {
+  rmSync(cache, { recursive: true, force: true })
+  console.log('cleared:', cache)
+} else {
+  console.log('no cache dir:', cache)
+}