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

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+{
+  "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}}"
+  }
+}

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

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+{
+  "filter": "Filter",
+  "clear": "Clear",
+  "all": "All",
+  "rowsPerPage": "Rows per page",
+  "noOptions": "No options",
+  "empty": "Nothing to show.",
+  "pager": {
+    "prev": "Previous",
+    "next": "Next",
+    "page": "Page {{page}} of {{total}}",
+    "pageLabel": "Page",
+    "ofTotal": "of {{total}}"
+  }
+}

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

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+{
+  "filter": "Szűrés",
+  "clear": "Törlés",
+  "all": "Mind",
+  "rowsPerPage": "Sor/oldal",
+  "noOptions": "Nincs lehetőség",
+  "empty": "Nincs megjeleníthető elem.",
+  "pager": {
+    "prev": "Előző",
+    "next": "Következő",
+    "page": "{{page}}. oldal / {{total}}",
+    "pageLabel": "Oldal",
+    "ofTotal": "/ {{total}}"
+  }
+}