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/nl/artists.ts

@@ -0,0 +1,18 @@
+export const artists = {
+  title: 'Artiesten',
+  search: 'Zoeken…',
+  all: 'Alle',
+  gridView: 'Rasterweergave',
+  listView: 'Lijstweergave',
+  imagesOn: 'Artiestafbeeldingen aan — kan netwerk- en systeembelasting verhogen',
+  imagesOff: 'Artiestafbeeldingen uit — toont alleen initialen',
+  loadMore: 'Meer laden',
+  notFound: 'Geen artiesten gevonden.',
+  albumCount_one: '{{count}} album',
+  albumCount_other: '{{count}} albums',
+  selectionCount: '{{count}} geselecteerd',
+  select: 'Meervoudige selectie',
+  startSelect: 'Meervoudige selectie inschakelen',
+  cancelSelect: 'Annuleren',
+  addToPlaylist: 'Toevoegen aan playlist',
+};