songs type label, disc header alignment, now playing back test

- Now Playing: the type line reads "songs" for the library songs list, source line stays "Library"
- Album detail: align the disc icon over the track numbers and the disc label with the track titles (16dp start + 18dp icon + 16dp gap, matching the ListItem columns)
- Add NowPlayingBackTest covering back-from-overlay not popping the destination

app/src/main/kotlin/com/subtracks/ui/library/AlbumDetailScreen.kt

@@ -149,15 +149,15 @@ fun AlbumDetailScreen(
 private fun DiscHeader(text: String) {
     Row(
         verticalAlignment = Alignment.CenterVertically,
-        modifier = Modifier.padding(start = 8.dp, end = 16.dp, top = 28.dp, bottom = 4.dp),
+        modifier = Modifier.padding(start = 16.dp, end = 16.dp, top = 28.dp, bottom = 4.dp),
     ) {
         Icon(
             imageVector = Icons.Outlined.FiberSmartRecord,
             contentDescription = null,
             tint = MaterialTheme.colorScheme.onSurfaceVariant,
-            modifier = Modifier.size(20.dp),
+            modifier = Modifier.size(18.dp),
         )
-        Spacer(Modifier.width(8.dp))
+        Spacer(Modifier.width(16.dp))
         Text(
             text = text.uppercase(),
             style = MaterialTheme.typography.labelLarge,

app/src/main/kotlin/com/subtracks/ui/playback/NowPlayingScreen.kt

@@ -402,7 +402,7 @@ private fun QueueKind.label(): String =
         QueueKind.Album -> "album"
         QueueKind.Playlist -> "playlist"
         QueueKind.Song -> "song"
-        QueueKind.Songs -> "library"
+        QueueKind.Songs -> "songs"
     }
 
 private fun formatTime(milliseconds: Long): String {

app/src/test/kotlin/com/subtracks/ui/NowPlayingBackTest.kt

@@ -0,0 +1,68 @@
+package com.subtracks.ui
+
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.BackHandler
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.material3.Text
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
+import androidx.compose.ui.test.onNodeWithText
+import androidx.navigation.NavHostController
+import androidx.navigation.compose.NavHost
+import androidx.navigation.compose.composable
+import androidx.navigation.compose.rememberNavController
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.github.takahirom.roborazzi.RobolectricDeviceQualifiers
+import org.junit.Assert.assertFalse
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.annotation.Config
+import org.robolectric.annotation.GraphicsMode
+
+@RunWith(AndroidJUnit4::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+@Config(qualifiers = RobolectricDeviceQualifiers.PixelXL)
+class NowPlayingBackTest {
+    @get:Rule
+    val composeRule = createAndroidComposeRule<ComponentActivity>()
+
+    @Test
+    fun backClosesTheOverlayBeforePoppingTheDestination() {
+        var overlayOpen by mutableStateOf(false)
+        var navController: NavHostController? = null
+        composeRule.setContent {
+            val nav = rememberNavController()
+            navController = nav
+            Box(Modifier.fillMaxSize()) {
+                NavHost(navController = nav, startDestination = "a") {
+                    composable("a") { Text("A") }
+                    composable("b") { Text("B") }
+                }
+                if (overlayOpen) {
+                    Text("OVERLAY", modifier = Modifier.fillMaxSize())
+                }
+            }
+            // Same ordering as MainNavigation: the overlay's back handler is registered after the
+            // NavHost, so it must consume back and leave the destination in place.
+            BackHandler(enabled = overlayOpen) {
+                overlayOpen = false
+            }
+        }
+
+        composeRule.runOnIdle { navController!!.navigate("b") }
+        composeRule.onNodeWithText("B").assertExists()
+        composeRule.runOnIdle { overlayOpen = true }
+        composeRule.onNodeWithText("OVERLAY").assertExists()
+
+        composeRule.runOnIdle { composeRule.activity.onBackPressedDispatcher.onBackPressed() }
+        composeRule.waitForIdle()
+
+        assertFalse("the overlay should have closed", overlayOpen)
+        composeRule.onNodeWithText("B").assertExists()
+    }
+}