refactor(i18n): split locale files into per-namespace modules (Phase K) (#688)

Each src/locales/<lang>.ts (~1800 LOC) becomes a folder src/locales/<lang>/
with one module per i18n namespace (44 each) plus an index.ts barrel that
reassembles <lang>Translation in the original key order.

Mechanical, script-driven split with a JSON round-trip check: every
locale object is byte-identical to its pre-split form. i18n.ts is
unchanged — './locales/<lang>' now resolves to the folder index.

The per-namespace settings.ts files land ~440-460 LOC; a single i18n
namespace is the natural, non-arbitrary split unit for a flat string
table, so they are intentionally left whole.

src/locales/de/radio.ts

@@ -0,0 +1,35 @@
+export const radio = {
+  title: 'Internetradio',
+  empty: 'Keine Radiosender konfiguriert.',
+  addStation: 'Sender hinzufügen',
+  editStation: 'Bearbeiten',
+  deleteStation: 'Sender löschen',
+  confirmDelete: 'Zum Bestätigen erneut klicken',
+  stationName: 'Sendername…',
+  streamUrl: 'Stream-URL…',
+  homepageUrl: 'Homepage-URL (optional)',
+  save: 'Speichern',
+  cancel: 'Abbrechen',
+  live: 'LIVE',
+  liveStream: 'Internetradio',
+  openHomepage: 'Homepage öffnen',
+  changeCoverLabel: 'Cover ändern',
+  removeCover: 'Cover entfernen',
+  browseDirectory: 'Verzeichnis durchsuchen',
+  directoryPlaceholder: 'Sender suchen…',
+  noResults: 'Keine Sender gefunden.',
+  stationAdded: 'Sender hinzugefügt',
+  filterAll: 'Alle',
+  filterFavorites: 'Favoriten',
+  sortManual: 'Manuell',
+  sortAZ: 'A → Z',
+  sortZA: 'Z → A',
+  sortNewest: 'Neueste',
+  favorite: 'Zu Favoriten hinzufügen',
+  unfavorite: 'Aus Favoriten entfernen',
+  noFavorites: 'Keine Lieblingssender.',
+  listenerCount_one: '{{count}} Hörer',
+  listenerCount_other: '{{count}} Hörer',
+  recentlyPlayed: 'Zuletzt gespielt',
+  upNext: 'Als Nächstes',
+};