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/Http/Requests/Admin/UpdateMailwizzConfigRequest.php

@@ -42,6 +42,7 @@ class UpdateMailwizzConfigRequest extends FormRequest
             'field_first_name' => ['required', 'string', 'max:255'],
             'field_last_name' => ['required', 'string', 'max:255'],
             'field_phone' => ['nullable', 'string', 'max:255'],
+            'field_coupon_code' => ['nullable', 'string', 'max:255'],
             'tag_field' => ['required', 'string', 'max:255'],
             'tag_value' => ['required', 'string', 'max:255'],
         ];