fix(ticketing): restrict settings link to admins and protect global priorities

- Show 'Go to Settings' bootstrap link only for admin/super_admin users
- Pass isSiteAdmin prop to Create.vue to control settings CTA visibility
- Require site admin for updatePriority/destroyPriority when priority is global (group_id = null)
- Closes: non-admin users seeing forbidden settings link; agents mutating global priorities

src/Http/Controllers/TicketingSettingsController.php

@@ -235,6 +235,11 @@ class TicketingSettingsController extends Controller
 
         if ($priority->group_id) {
             $this->requireManagerAccess($priority->group_id);
+        } else {
+            // Global priorities require site admin
+            if (!$this->isSiteAdmin()) {
+                abort(403, 'Only site admins can manage global priorities.');
+            }
         }
 
         $validated = $request->validate([
@@ -264,6 +269,11 @@ class TicketingSettingsController extends Controller
 
         if ($priority->group_id) {
             $this->requireManagerAccess($priority->group_id);
+        } else {
+            // Global priorities require site admin
+            if (!$this->isSiteAdmin()) {
+                abort(403, 'Only site admins can manage global priorities.');
+            }
         }
 
         if ($priority->tickets()->exists()) {