fix(notification): allow clearing the sound on per-app overrides and main row

Previously, both the per-app override sound dropdown and the main
notification sound row only attached an EntitySelect when at least
one sound asset was registered — and never with allowNone. That left
users with no way to pick "no sound" once an entry existed, and made
the override dropdown silently inert before any assets were added.

Always construct the EntitySelect (so an empty assets list still
renders a usable, searchable input) and pass allowNone with the
localized none label so "no sound" is a first-class choice in both
the override list and the main row.

server/src/ledgrab/static/js/features/color-strips/notification.ts

@@ -233,15 +233,14 @@ function _overridesRenderList() {
 
     // Wire EntitySelects for sound dropdowns
     list.querySelectorAll<HTMLSelectElement>('.notif-override-sound').forEach(sel => {
-        const items = _getSoundAssetItems();
-        if (items.length > 0) {
         const es = new EntitySelect({
             target: sel,
             getItems: () => _getSoundAssetItems(),
             placeholder: t('color_strip.notification.sound.search') || 'Search sounds…',
+            allowNone: true,
+            noneLabel: t('color_strip.notification.sound.none'),
         });
         _overrideEntitySelects.push(es);
-        }
     });
 }
 
@@ -300,14 +299,13 @@ export function ensureNotifSoundEntitySelect() {
     if (!sel) return;
     _populateSoundOptions(sel);
     if (_notifSoundEntitySelect) _notifSoundEntitySelect.destroy();
-    const items = _getSoundAssetItems();
-    if (items.length > 0) {
     _notifSoundEntitySelect = new EntitySelect({
         target: sel,
         getItems: () => _getSoundAssetItems(),
         placeholder: t('color_strip.notification.sound.search') || 'Search sounds…',
+        allowNone: true,
+        noneLabel: t('color_strip.notification.sound.none'),
     });
-    }
 }
 
 /* ── Test notification ────────────────────────────────────────── */