feat(loyalty): make logo URL mandatory on program edit forms

Logo URL is required by Google Wallet API for LoyaltyClass creation.
Added validation across all three program edit screens (admin, merchant, store)
with a helpful hint explaining the requirement.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/loyalty/templates/loyalty/shared/program-form.html

@@ -226,9 +226,10 @@
             </div>
         </div>
         <div>
-            <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-2">Logo URL</label>
-            <input type="url" x-model="settings.logo_url" maxlength="500" placeholder="https://..."
+            <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-2">Logo URL <span class="text-red-500">*</span></label>
+            <input type="url" x-model="settings.logo_url" maxlength="500" placeholder="https://..." required
                    class="w-full px-4 py-2 text-sm border border-gray-300 dark:border-gray-600 rounded-lg focus:border-purple-400 focus:outline-none dark:bg-gray-700 dark:text-gray-300">
+            <p class="mt-1 text-xs text-gray-500 dark:text-gray-400">Required for Google Wallet integration. Must be a publicly accessible image URL (PNG or JPG).</p>
         </div>
         <div>
             <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-2">Hero Image URL</label>