feat: add Weeztix OAuth, coupon codes, and Mailwizz mapping

Implement Weeztix integration per documentation: database config and
subscriber coupon_code, OAuth redirect/callback, admin setup UI with
company/coupon selection via AJAX, synchronous coupon creation on public
subscribe with duplicate and rate-limit handling, Mailwizz field mapping
for coupon codes, subscriber table and CSV export, and connection hint
on the pages list.

Made-with: Cursor

app/Models/Subscriber.php

@@ -22,6 +22,7 @@ class Subscriber extends Model
         'phone',
         'synced_to_mailwizz',
         'synced_at',
+        'coupon_code',
     ];
 
     protected function casts(): array
@@ -95,7 +96,8 @@ class Subscriber extends Model
             $q->where('first_name', 'like', $like)
                 ->orWhere('last_name', 'like', $like)
                 ->orWhere('email', 'like', $like)
-                ->orWhere('phone', 'like', $like);
+                ->orWhere('phone', 'like', $like)
+                ->orWhere('coupon_code', 'like', $like);
         });
     }
 }