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/en/randomMix.ts

@@ -0,0 +1,39 @@
+export const randomMix = {
+  title: 'Random Mix',
+  remix: 'Remix',
+  remixTooltip: 'Load new random songs',
+  remixGenre: 'Remix {{genre}}',
+  remixTooltipGenre: 'Load new {{genre}} songs',
+  playAll: 'Play All',
+  trackTitle: 'Title',
+  trackArtist: 'Artist',
+  trackAlbum: 'Album',
+  trackFavorite: 'Favorite',
+  trackDuration: 'Duration',
+  favoriteAdd: 'Add to Favorites',
+  favoriteRemove: 'Remove from Favorites',
+  play: 'Play',
+  trackGenre: 'Genre',
+  mixSettingsHeader: 'Mix Settings',
+  exclusionsHeader: 'Exclusions',
+  filterPanelInexactSizeNote: 'Mix size is a target — large requests may return fewer unique tracks if the server\'s random pool runs short.',
+  mixSize: 'Playlist size',
+  excludeAudiobooks: 'Exclude audiobooks & radio plays',
+  excludeAudiobooksDesc: 'Matches keywords against genre, title, album, and artist — e.g. Hörbuch, Audiobook, Spoken Word, …',
+  genreBlocked: 'Keyword blocked',
+  genreAddedToBlacklist: 'Added to filter list',
+  genreAlreadyBlocked: 'Already blocked',
+  artistBlocked: 'Artist blocked',
+  artistAddedToBlacklist: 'Artist added to filter list',
+  artistClickHint: 'Click to block this artist',
+  blacklistToggle: 'Keyword Filter',
+  genreMixTitle: 'Genre Mix',
+  genreMixDesc: 'Top 20 genres by song count — click to load a random mix',
+  genreMixAll: 'All Songs',
+  genreMixLoadMore: 'Load 10 more',
+  genreMixNoGenres: 'No genres found on server.',
+  shuffleGenres: 'Show different genres',
+  filterPanelTitle: 'Filters',
+  filterPanelDesc: 'Click a genre tag or artist name in the tracklist below to block it from future mixes.',
+  genreClickHint: 'Click a genre tag to add it\nas a filter keyword.\nMatches genre, title, album & artist.',
+};