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/miniPlayer.ts

@@ -0,0 +1,9 @@
+export const miniPlayer = {
+  showQueue: 'Warteschlange einblenden',
+  hideQueue: 'Warteschlange ausblenden',
+  pinOnTop: 'Im Vordergrund halten',
+  pinOff: 'Vordergrund deaktivieren',
+  openMainWindow: 'Hauptfenster öffnen',
+  close: 'Schließen',
+  emptyQueue: 'Die Warteschlange ist leer',
+};