fix(statistics): accurate counts for large libraries + album-artist tooltip

Remove the 10-page cap in fetchStatisticsLibraryAggregates — the loop now runs until
the server returns a partial page, so albums/songs/playtime reflect the full library
regardless of size (previously capped at 5,000 albums). Switched sort type from
'newest' to 'alphabeticalByName' for a stable pagination order.

Add a tooltip on the Artists stat card explaining it shows album artists only (Subsonic
API limitation — track-level featured/guest artists without their own album are not
included). Tooltip added in all 8 locales. Labels with a tooltip get a dotted underline
and cursor:help as visual hint.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/zh.ts

@@ -779,6 +779,7 @@ export const zhTranslation = {
     genreDistribution: '流派分布（前 20）',
     loadMore: '加载更多',
     statArtists: '艺术家',
+    statArtistsTooltip: '仅限专辑艺术家——仅作为单曲艺术家出现（合唱、客串等）且无自己专辑的艺术家不计入此处。',
     statAlbums: '专辑',
     statSongs: '歌曲',
     statGenres: '流派',