Add command palette entity selector for all editor dropdowns

Replace plain <select> dropdowns with a searchable command palette modal
for 16 entity selectors across 6 editors (targets, streams, CSS sources,
value sources, audio sources, pattern templates). Unified EntityPalette
singleton + EntitySelect wrapper in core/entity-palette.js.

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

server/src/wled_controller/static/locales/en.json

@@ -323,6 +323,7 @@
   "common.edit": "Edit",
   "common.clone": "Clone",
   "common.none": "None",
+  "palette.search": "Search…",
   "section.filter.placeholder": "Filter...",
   "section.filter.reset": "Clear filter",
   "section.expand_all": "Expand all sections",

server/src/wled_controller/static/locales/ru.json

@@ -323,6 +323,7 @@
   "common.edit": "Редактировать",
   "common.clone": "Клонировать",
   "common.none": "Нет",
+  "palette.search": "Поиск…",
   "section.filter.placeholder": "Фильтр...",
   "section.filter.reset": "Очистить фильтр",
   "section.expand_all": "Развернуть все секции",

server/src/wled_controller/static/locales/zh.json

@@ -323,6 +323,7 @@
   "common.edit": "编辑",
   "common.clone": "克隆",
   "common.none": "无",
+  "palette.search": "搜索…",
   "section.filter.placeholder": "筛选...",
   "section.filter.reset": "清除筛选",
   "section.expand_all": "全部展开",