feat(forum): guest cash purchase for topic and plate follow

- Reuse pay_no_logged_in / pay_cookie_day; generalized guest cookie helpers
- Topic + plate cash: guest preview/purchase (no balance), order.user_id=0, cookie unlock
- View gates: can_view_topic pay + plate follow accept signed guest cookies
- Templates: guest buy/follow CTAs; poll endpoint allows plate_follow guest orders

inc/classes/forum/topic-service-traits/trait-aksrt-forum-topic-service-part-3.php

@@ -220,7 +220,8 @@ trait AKSRT_Forum_Topic_Service_Part_3 {
 
         if ($visibility === AKSRT_Forum::VISIBILITY_PAY) {
             if ($viewer_user_id <= 0) {
-                return false;
+                return function_exists('aksrt_guest_has_paid_access')
+                    && aksrt_guest_has_paid_access((int) $post->ID);
             }
             return $this->has_user_paid_topic($viewer_user_id, (int) $post->ID);
         }
@@ -514,9 +515,12 @@ trait AKSRT_Forum_Topic_Service_Part_3 {
      * Paid access for VISIBILITY_PAY: unlock list OR paid resource order OR VIP free.
      */
     public function has_user_paid_topic(int $user_id, int $topic_id): bool {
-        if ($user_id <= 0 || $topic_id <= 0) {
+        if ($topic_id <= 0) {
             return false;
         }
+        if ($user_id <= 0) {
+            return function_exists('aksrt_guest_has_paid_access') && aksrt_guest_has_paid_access($topic_id);
+        }
 
         if ($this->has_user_unlocked_topic($user_id, $topic_id)) {
             return true;