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/de.ts

@@ -785,6 +785,7 @@ export const deTranslation = {
     genreDistribution: 'Genre-Verteilung (Top 20)',
     loadMore: 'Mehr laden',
     statArtists: 'Künstler',
+    statArtistsTooltip: 'Nur Album-Künstler — Künstler, die ausschließlich als Track-Künstler vorkommen (Featured, Gast usw.) und kein eigenes Album haben, werden nicht gezählt.',
     statAlbums: 'Alben',
     statSongs: 'Songs',
     statGenres: 'Genres',