feat(upload): pending lifecycle for upload-on-select images

Mark front-end uploads (comment/ticket/report) as pending, return the
attachment id, discard own pending uploads on remove via
DELETE /upload/pending/{id}, claim referenced URLs on successful submit,
and purge unclaimed uploads older than 24h with an hourly cron.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/Ticket/TicketRestAdmin.php

@@ -337,6 +337,7 @@ final class TicketRestAdmin {
         if ($id <= 0) {
             return new \WP_Error('aksrt_ticket_db', __('工单创建失败', 'aksrt'), ['status' => 500]);
         }
+        \AKSRT\Attachment\PendingUploads::claim_urls($attachment, get_current_user_id());
         $ticket = TicketRepository::get_instance()->find($id);
         if (is_array($ticket)) {
             TicketNotifier::user_replied($ticket);
@@ -371,6 +372,7 @@ final class TicketRestAdmin {
         if ($reply_id <= 0) {
             return new \WP_Error('aksrt_ticket_db', __('回复提交失败', 'aksrt'), ['status' => 500]);
         }
+        \AKSRT\Attachment\PendingUploads::claim_urls($attachment, get_current_user_id());
         $repo->touch_reply($id, 'admin', get_current_user_id());
         $repo->apply_reply_status($id, $ticket, 'admin');
         TicketNotifier::user_replied($repo->find($id) ?? $ticket);