refactor(admin): drop AI connection config page for WP AI Connectors

Remove the "AI 连接配置" page under 扩展&增强 together with the theme's
own OpenAI-compatible provider path. AI generation (SEO, summary, tags)
now runs solely on the WordPress AI Client (wp_ai_client_prompt), with
connections configured through WordPress AI Connectors.

- AI.php keeps only the WP AI Client path: no provider config storage,
  no theme fallback, no rate limiting
- Drop /ai/status, /ai/settings and legacy /ai/seo-suggest routes plus
  their handlers
- Remove dead compat code: AISEO::suggest, AIPrompt::build_seo_prompt
  and the front-submit AI assist flow (its buttons were never rendered
  and its endpoints were never registered)
- Update SEO schema/meta-box guidance that pointed at the deleted page
- Add ai-config-removal contract test and refresh the toast and
  user-features contracts affected by the cleanup

assets/js/front-submit.js

@@ -103,7 +103,6 @@
       this.bindFeatured();
       this.bindPay();
       this.bindLeaveWarning();
-      this.bindAi();
       this.bindTagActive();
       this.loadFeaturedFromDom();
     },
@@ -635,67 +634,6 @@
       });
     },
 
-    bindAi: function () {
-      var ai = cfg.ai || {};
-      if (!ai.available) {
-        return;
-      }
-      qsa('.aksrt-ai-assist-btn').forEach(function (btn) {
-        btn.hidden = false;
-        btn.addEventListener('click', function () {
-          var action = btn.getAttribute('data-ai-action');
-          var content = getEditorContent();
-          if (!content || content.replace(/<[^>]+>/g, '').trim().length < 10) {
-            notyf(i18n.needContent || '请先填写正文内容', 'warning');
-            return;
-          }
-          var toastId = action === 'tags'
-            ? 'aksrt-front-submit-ai-tags-toast'
-            : 'aksrt-front-submit-ai-summary-toast';
-          var old = btn.textContent;
-          btn.disabled = true;
-          btn.textContent = i18n.aiGenerating || '...';
-          notyf(i18n.aiGenerating || '正在生成…', 'load', '', toastId);
-          fetch((cfg.restUrl || '').replace(/\/$/, '') + '/ai/' + action, {
-            method: 'POST',
-            credentials: 'same-origin',
-            headers: {
-              'Content-Type': 'application/json',
-              'X-WP-Nonce': cfg.restNonce || '',
-            },
-            body: JSON.stringify({ content: content }),
-          })
-            .then(function (r) {
-              return r.json();
-            })
-            .then(function (res) {
-              var text = (res && (res.data || res).text) || (res && res.result) || '';
-              if (!text) {
-                throw new Error(i18n.aiFailed || 'AI failed');
-              }
-              if (action === 'summary') {
-                var ex = qs('[name="excerpt"]');
-                if (ex) {
-                  ex.value = text;
-                }
-              } else if (action === 'tags') {
-                var tags = qs('[name="tags"]');
-                if (tags) {
-                  tags.value = text;
-                }
-              }
-              notyf(i18n.aiFilled || '已填入，可继续编辑', 'success', 5, toastId);
-            })
-            .catch(function (err) {
-              notyf(err.message || i18n.aiFailed || 'AI 生成失败', 'danger', 5, toastId);
-            })
-            .finally(function () {
-              btn.disabled = false;
-              btn.textContent = old;
-            });
-        });
-      });
-    },
   };
 
   jQuery(document).off('auto_fun.aksrt-front-submit').on('auto_fun.aksrt-front-submit', function () { App.init(); });