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/luckyMix.ts

@@ -0,0 +1,6 @@
+export const luckyMix = {
+  done: 'Glücks-Mix bereit: {{count}} Titel',
+  failed: 'Glücks-Mix konnte nicht erstellt werden. Bitte erneut versuchen.',
+  unavailable: 'Glücks-Mix ist für diesen Server nicht verfügbar.',
+  cancelTooltip: 'Glücks-Mix-Erstellung abbrechen',
+};