feat: partial album split view + artist page full-screen + Bibliothek iTunes integration

- Partial album detail: tapping incomplete albums now shows downloaded songs
  (normal playback) above and missing iTunes tracks (30s preview + download)
  below — on both Android and web PWA
- Android: ItunesArtistScreen now renders full-screen above the tab/search bar
- Android: ArtistDetailScreen (Bibliothek) now loads iTunes data in parallel —
  adds Weltweit populär section and In Library/Unvollständig/Nicht heruntergeladen
  album sections identical to the Erkunden artist page
- Fix: artist no longer appears in its own Similar Artists row
- Fix: duplicate album entries deduplicated by collectionId in categorizeAlbums

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

android/build.gradle.kts

@@ -1,4 +1,7 @@
 plugins {
-    alias(libs.plugins.android.application) apply false
-    alias(libs.plugins.kotlin.android) apply false
+    alias(libs.plugins.android.application)  apply false
+    alias(libs.plugins.kotlin.android)       apply false
+    alias(libs.plugins.kotlin.compose)       apply false
+    alias(libs.plugins.kotlin.serialization) apply false
+    alias(libs.plugins.ksp)                  apply false
 }