feat: EntityPicker component, replace dropdowns with command palette

Port EntityPalette pattern from wled-screen-controller as Svelte 5
component. Full-screen modal with search, keyboard navigation
(Arrow keys, Enter, Escape), grouped items, current-item accent,
auto-scroll, backdrop blur.

Replace inline image browser dropdowns on Projects and Quick Deploy
pages with EntityPicker. Add EntityPickerItem type and i18n keys.

web/src/lib/i18n/en.json

@@ -376,6 +376,10 @@
     "dark": "Dark",
     "system": "System"
   },
+  "entityPicker": {
+    "search": "Search...",
+    "noResults": "No results found"
+  },
   "language": {
     "en": "English",
     "ru": "Russian"