chore: 移除 LeetCode 笔记并加入站点验证与 Agent 工作流规则

- 从 collections、导航移除 LeetCode，删除 docs/notes/programming/leetcode 下页面

- devDependencies 显式加入 @vuepress/helper@rc.123，配合 overrides 降低 Vite 预构建白屏风险

- 新增 npm run docs:verify 与 scripts/verify-site.mjs（构建后检查首页 hero）

- .cursor/rules/agent-workflow-verify-and-git.mdc：每次修改须验证；用户未明确说不要提交时默认 commit

Made-with: Cursor

package-lock.json

@@ -15,6 +15,7 @@
       },
       "devDependencies": {
         "@vuepress/bundler-vite": "2.0.0-rc.26",
+        "@vuepress/helper": "2.0.0-rc.123",
         "@vuepress/plugin-umami-analytics": "2.0.0-rc.112",
         "artalk": "^2.9.1",
         "http-server": "^14.1.1",