feat(captcha): 打通人机验证 11 个场景的前后端完整链路

- 统一验证入口 aksrt_require_captcha()，返回 true|WP_Error，启用场景配置缺失时 fail-closed 拒绝
- 前端公共 API 重构为 window.AKSRTCaptcha（verify/collect/reset/run），单飞锁防并发重复验证，一次性 proof 绑定浏览器 cookie+场景+服务商+主机名
- challenge/exchange REST 端点：challenge 原子占用防票据放大厂商调用，增加频率限制
- 新增 OAuth bind pass：服务端签发 5 分钟一次性令牌，绑定用户+服务商+浏览器，微信扫码延迟消费
- 覆盖场景：评论、登录、注册、绑定第三方、绑定手机、找回密码、修改密码、更改邮箱、资料下载、签到、前台投稿
- 移除 Service 层重复验证与 _auth_code_verified/_defer_login 等客户端可伪造标志，删除下载共享 pass 死代码
- 修复腾讯 TC3 签名 scope、Cloudflare action/cdata/hostname 严格校验、阿里云验签错误码映射
- 后台 Schema 保存对 secret 字段做掩码/保留合并；导入导出过滤 aksrt_captcha_config
- 重建 public bundle 与 admin SPA；新增 captcha 运行时/安全/业务契约测试与 harness

tests/widget-system/front-submit-editor-contract.test.cjs

@@ -105,6 +105,18 @@ test('public theme does not inject a global focus-visible ring', () => {
   assert.doesNotMatch(publicMinCss, globalFocusRule);
 });
 
+test('non-draft front-submit updates require one server captcha admission', () => {
+  const controller = read('src/Core/FrontSubmit.php');
+  const start = controller.indexOf('public function ajax_update_post(): void');
+  const end = controller.indexOf('\n    public function ajax_delete_draft', start);
+  const body = controller.slice(start, end);
+
+  assert.match(body, /\$action = \(\(\$data\['status'\] \?\? ''\) === 'draft'\) \? 'posts_draft' : 'posts_save';/);
+  assert.match(body, /if \(\$action !== 'posts_draft'\) \{\s*\$this->verify_captcha\(\);\s*\}/);
+  assert.match(controller, /get_error_code\(\)/);
+  assert.match(controller, /get_error_message\(\)/);
+});
+
 test('front submit TinyMCE status bar shows one live character counter', () => {
   const editor = read('assets/js/front-submit-editor.js');
   const submitCss = read('assets/css/frontend/pages/submit.css');