feat(ai): 打通 SEO 闭环与投稿写作辅助

对齐 Zibll 的 AI 生成 SEO 流程：统一 WP AI Client/主题 Provider 双后端、文章/分类 SEO 框与生成回填、投稿摘要/标签建议，并收敛扩展页为连接配置。

inc/classes/class-aksrt-seo-head.php

@@ -126,9 +126,20 @@ class AKSRT_SEO_Head {
             $term = get_queried_object();
             if ($term instanceof WP_Term) {
                 $payload['canonical'] = (string) get_term_link($term);
-                $term_desc = trim(wp_strip_all_tags((string) term_description($term)));
-                if ($term_desc !== '') {
-                    $payload['description'] = $term_desc;
+                $meta = $this->term_seo_meta((int) $term->term_id);
+                if ($meta['title'] !== '') {
+                    $payload['title'] = $meta['title'];
+                }
+                if ($meta['description'] !== '') {
+                    $payload['description'] = $meta['description'];
+                } else {
+                    $term_desc = trim(wp_strip_all_tags((string) term_description($term)));
+                    if ($term_desc !== '') {
+                        $payload['description'] = $term_desc;
+                    }
+                }
+                if ($meta['keywords'] !== '') {
+                    $payload['keywords'] = $meta['keywords'];
                 }
             }
         }
@@ -163,6 +174,23 @@ class AKSRT_SEO_Head {
         ];
     }
 
+    /**
+     * 读取 term SEO 覆盖。
+     *
+     * @return array{title:string,description:string,keywords:string}
+     */
+    private function term_seo_meta(int $term_id): array {
+        $get = static function (string $key) use ($term_id): string {
+            return trim((string) get_term_meta($term_id, $key, true));
+        };
+
+        return [
+            'title'       => $get('_aksrt_seo_title'),
+            'description' => $get('_aksrt_seo_description'),
+            'keywords'    => $get('_aksrt_seo_keywords'),
+        ];
+    }
+
     /**
      * 由分类/标签生成关键词回退。
      */