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

docs/.vuepress/navbar.ts

@@ -25,10 +25,6 @@ export default defineNavbarConfig([
   {
     text: '编程笔记',
     items: [
-      {
-        text: 'LeetCode',
-        link: '/programming/leetcode/',
-      },
       {
         text: 'Solidity',
         link: '/programming/solidity/',