fix: ABS skip library list + nav label overflow + NowPlaying top bar + dominant color bg

- ABS: new AbsBooksScreen loads books directly on tab open; library pills shown only when >1 library — no more two-step library→books navigation
- Nav: shorten "Hörbücher"→"Bücher", "Einstellungen"→"Einst.", reduce label font to 9sp with maxLines=1 to prevent label wrapping
- NowPlaying: increase top padding so the tab bar sits lower on screen (statusBarTop + 16dp, min 52dp)
- NowPlaying: replace blurred-cover background with dominant-color gradient extracted via Palette from cover art; animates on track change; falls back to dark color

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

android/app/build.gradle.kts

@@ -93,6 +93,9 @@ dependencies {
     // Coil
     implementation(libs.coil.compose)
 
+    // Palette (dominant cover color extraction in NowPlaying)
+    implementation("androidx.palette:palette-ktx:1.0.0")
+
     // Google Fonts (Outfit)
     implementation(libs.compose.ui.google.fonts)
 }