feat(launcher): add launcher_menu/header/footer URL params to URL builder; strip after apply

src/routes/events/[event_id]/(launcher)/launcher/+layout.svelte

@@ -147,6 +147,22 @@
             if (param_launcher_footer === 'hide')  $events_loc.launcher.hide__launcher_footer = true;
             else if (param_launcher_footer === 'show') $events_loc.launcher.hide__launcher_footer = false;
         });
+
+        // Strip launcher display params from the URL after applying them — same pattern
+        // as root layout does for ?theme / ?theme_mode.  These are "one-shot" apply params;
+        // keeping them in the URL is misleading because toggling the CFG panel would desync.
+        // ?iframe is intentionally left in the URL because it is a persistent mode flag.
+        if (param_launcher_menu || param_launcher_header || param_launcher_footer) {
+            const clean_url = new URL(data.url.href);
+            clean_url.searchParams.delete('launcher_menu');
+            clean_url.searchParams.delete('launcher_header');
+            clean_url.searchParams.delete('launcher_footer');
+            goto(clean_url.pathname + clean_url.search + clean_url.hash, {
+                replaceState: true,
+                noScroll: true,
+                keepFocus: true
+            });
+        }
     });
 
     // String-Only ID Vision: Sync the device ID from the native environment