feat(ui): reusable DataTable component

Generic client-side table: per-column sort, in-header filters (text/select/multi),
built-in pagination with a user-set page size (incl. All) and an editable jump-to-page
box. Sort/filter/page/size persist to localStorage (survive F5). Falls back to a compact
card list below md. Intended for reuse across modules (channels now, playlists next).

frontend/src/i18n/locales/de/datatable.json

@@ -0,0 +1,15 @@
+{
+  "filter": "Filtern",
+  "clear": "Löschen",
+  "all": "Alle",
+  "rowsPerPage": "Zeilen pro Seite",
+  "noOptions": "Keine Optionen",
+  "empty": "Nichts anzuzeigen.",
+  "pager": {
+    "prev": "Zurück",
+    "next": "Weiter",
+    "page": "Seite {{page}} von {{total}}",
+    "pageLabel": "Seite",
+    "ofTotal": "von {{total}}"
+  }
+}