fix(loyalty): drop unregistered device-tablet icon, guard QR template against null

- The icon registry has no 'device-tablet' (closest available is 'phone',
  which is already used for similar device-mobile contexts). Replace
  uses I added in the merchant menu item and the empty state.

- The pairing-QR modal uses x-show on the QR/payload blocks, but x-show
  only toggles display while Alpine still evaluates child expressions.
  pairingResult is null on first render, so the template threw "can't
  access property 'qr_png_base64'/'setup_payload', pairingResult is
  null" until pairing actually fired. Wrap the block in
  <template x-if="pairingResult"> so the bindings only mount when the
  data exists.

(There is a third 'device-tablet' reference in store/analytics.html
that predates this work — leaving it for a separate cleanup since
it's not on the Android-rollout path.)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/modules/loyalty/definition.py

@@ -282,7 +282,7 @@ loyalty_module = ModuleDefinition(
                     MenuItemDefinition(
                         id="devices",
                         label_key="loyalty.menu.terminal_devices",
-                        icon="device-tablet",
+                        icon="phone",
                         route="/merchants/loyalty/devices",
                         order=32,
                     ),

app/modules/loyalty/templates/loyalty/shared/devices-list.html

@@ -55,7 +55,7 @@
                 <tr>
                     <td :colspan="'{{ '6' if show_store_filter else '5' }}'" class="px-4 py-8 text-center text-gray-600 dark:text-gray-400">
                         <div class="flex flex-col items-center">
-                            <span x-html="$icon('device-tablet', 'w-12 h-12 mb-2 text-gray-300')"></span>
+                            <span x-html="$icon('phone', 'w-12 h-12 mb-2 text-gray-300')"></span>
                             <p class="font-medium">{{ _('loyalty.terminal_devices.no_devices') }}</p>
                         </div>
                     </td>
@@ -150,13 +150,17 @@
                 {{ _('loyalty.terminal_devices.qr_warning_body') }}
             </p>
         </div>
-        <div class="flex items-center justify-center bg-white p-4 rounded-lg" x-show="pairingResult">
+        <template x-if="pairingResult">
+            <div>
+                <div class="flex items-center justify-center bg-white p-4 rounded-lg">
                     <img :src="pairingResult.qr_png_base64" alt="Pairing QR code" class="w-64 h-64">
                 </div>
-        <details class="text-sm" x-show="pairingResult">
+                <details class="text-sm mt-3">
                     <summary class="cursor-pointer text-gray-600 dark:text-gray-400">{{ _('loyalty.terminal_devices.show_payload') }}</summary>
                     <pre class="mt-2 p-3 text-xs bg-gray-50 dark:bg-gray-900 rounded overflow-x-auto" x-text="JSON.stringify(pairingResult.setup_payload, null, 2)"></pre>
                 </details>
+            </div>
+        </template>
         <div class="flex items-center justify-end">
             <button @click="closeQrModal()" type="button"
                     class="px-4 py-2 text-sm font-medium text-white bg-purple-600 rounded-lg hover:bg-purple-700">