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/zh/search.ts

@@ -0,0 +1,29 @@
+export const search = {
+  placeholder: '搜索艺术家、专辑或歌曲…',
+  noResults: '未找到 "{{query}}" 的相关结果',
+  artists: '艺术家',
+  albums: '专辑',
+  songs: '歌曲',
+  clearLabel: '清除搜索',
+  addedToQueueToast: '已将"{{title}}"加入队列',
+  title: '搜索',
+  resultsFor: '"{{query}}" 的搜索结果',
+  album: '专辑',
+  advanced: '高级搜索',
+  advancedSearchTerm: '搜索词',
+  advancedSearchPlaceholder: '标题、专辑、艺术家…',
+  advancedGenre: '流派',
+  advancedAllGenres: '所有流派',
+  advancedYear: '年份',
+  advancedYearFrom: '从',
+  advancedYearTo: '至',
+  advancedAll: '全部',
+  advancedSearch: '搜索',
+  advancedEmpty: '请输入搜索词或选择过滤器。',
+  advancedNoResults: '未找到结果。',
+  advancedGenreNote: '歌曲从该流派中随机选取。',
+  recentSearches: '最近搜索',
+  browse: '浏览',
+  emptyHint: '你想听什么？',
+  genres: '流派',
+};