feat(launcher): restore macOS default wallpaper + external-only apply fix

- electron_relay: add restore_macos_default_wallpaper() — uses run_osascript
  to find first .heic in /System/Library/Desktop Pictures/ (version-agnostic)
- wallpaper cfg: Restore macOS Default button (native or edit_mode); clears
  applied-URL tracking so next configured URL re-applies correctly
- wallpaper cfg: fix Apply Now / Save & Apply enabled when only external URL
  is filled; display target becomes 'external' to leave built-in unchanged

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

src/lib/electron/electron_relay.ts

@@ -413,6 +413,38 @@ export async function set_wallpaper({
     return await native.set_wallpaper({ path, url, url_external, display, api_key, account_id });
 }
 
+/**
+ * Restores the macOS default wallpaper on all displays.
+ * Scans /System/Library/Desktop Pictures/ for the first .heic file — works across
+ * all recent macOS versions without needing to know the version name.
+ * No-op on non-macOS (Linux/Windows return success:false from run_osascript).
+ */
+export async function restore_macos_default_wallpaper(
+    display: 'all' | 'primary' | 'external' = 'all'
+): Promise<{ success: boolean; error?: string }> {
+    const display_target =
+        display === 'primary'
+            ? 'tell desktop 1'
+            : display === 'external'
+              ? 'tell desktop 2'
+              : 'tell every desktop';
+
+    const script = `
+set pic_path to do shell script "ls '/System/Library/Desktop Pictures/'*.heic 2>/dev/null | head -1"
+if pic_path is "" then
+    error "No default macOS wallpaper (.heic) found in /System/Library/Desktop Pictures/"
+end if
+tell application "System Events"
+    ${display_target}
+        set picture to pic_path
+    end tell
+end tell
+`.trim();
+
+    const result = await run_osascript(script);
+    return result ?? { success: false, error: 'Native bridge not available' };
+}
+
 export async function update_app(args: {
     source: 'url' | 'file';
     url?: string;

src/routes/events/[event_id]/(launcher)/cfg_components/launcher_cfg_wallpaper.svelte

@@ -4,7 +4,7 @@ import { events_func } from '$lib/ae_events/ae_events_functions';
 import { events_loc } from '$lib/stores/ae_events_stores';
 import * as native from '$lib/electron/electron_relay';
 import Launcher_Cfg_Section from './launcher_cfg_section.svelte';
-import { FlaskConical, Image, Monitor, Save, Zap } from '@lucide/svelte';
+import { FlaskConical, Image, Monitor, RotateCcw, Save, Zap } from '@lucide/svelte';
 
 interface Props {
     on_expand?: () => void;
@@ -23,6 +23,7 @@ let url_input = $state('');
 let url_external_input = $state('');
 let save_status = $state('');
 let apply_status = $state('');
+let restore_status = $state('');
 let last_device_id: string | null = null;
 
 function get_native_device(): NativeDeviceLike | null {
@@ -148,6 +149,20 @@ async function handle_apply() {
     }
 }
 
+async function handle_restore_default() {
+    restore_status = 'Restoring...';
+    const result = await native.restore_macos_default_wallpaper('all');
+    if (result?.success) {
+        // Clear tracked applied URL so the next config URL re-applies correctly.
+        $events_loc.launcher.wallpaper_applied_url = null;
+        $events_loc.launcher.wallpaper_applied_url_external = null;
+        restore_status = 'Restored ✓';
+    } else {
+        restore_status = `Error: ${(result as any)?.error ?? 'Unknown error'}`;
+    }
+    setTimeout(() => { if (restore_status.startsWith('Restored') || restore_status.startsWith('Error')) restore_status = ''; }, 4000);
+}
+
 async function handle_save_and_apply() {
     await handle_save();
     if (save_status !== 'Save failed' && save_status !== 'No device loaded') {
@@ -276,6 +291,16 @@ const section_description = $derived(
             Save & Apply
         </button>
 
+        <!-- Restore macOS default — safety valve for end-of-show cleanup -->
+        {#if $ae_loc.is_native || $ae_loc.edit_mode}
+            <button
+                type="button"
+                onclick={handle_restore_default}
+                class="btn btn-sm preset-tonal-surface h-8 w-full text-[10px] opacity-60 hover:opacity-100">
+                <RotateCcw size="0.8em" class="mr-1" /> Restore macOS Default
+            </button>
+        {/if}
+
         {#if save_status}
             <div
                 class="text-primary-500 text-center text-[9px] italic"
@@ -292,5 +317,14 @@ const section_description = $derived(
                 {apply_status}
             </div>
         {/if}
+        {#if restore_status}
+            <div
+                class="text-[9px] italic text-center"
+                class:text-success-500={restore_status.includes('✓')}
+                class:text-primary-500={restore_status === 'Restoring...'}
+                class:text-error-500={restore_status.includes('Error')}>
+                {restore_status}
+            </div>
+        {/if}
     </div>
 </Launcher_Cfg_Section>