fix back popping the route under now playing; disc header spacing; dial back the fab glyph

- register the now playing and queue back callback from a LaunchedEffect instead of BackHandler: the NavHost registers its own callback from a LaunchedEffect, so a BackHandler composed before it loses the back and pops the route underneath
- NowPlayingBackTest registers the overlay handler before the NavHost (the losing order) and asserts back closes the overlay without popping the route
- more top padding on disc headers, except the first which sits flush
- LIST_OPTIONS_WEIGHT 0.15 -> 0.11

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

@@ -1,12 +1,21 @@
 package com.subtracks.ui
 
 import androidx.activity.ComponentActivity
-import androidx.activity.compose.BackHandler
+import androidx.activity.OnBackPressedCallback
+import androidx.activity.compose.LocalOnBackPressedDispatcherOwner
+import androidx.compose.animation.core.tween
+import androidx.compose.animation.fadeIn
+import androidx.compose.animation.fadeOut
+import androidx.compose.animation.slideInHorizontally
+import androidx.compose.animation.slideOutHorizontally
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.material3.Text
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.SideEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
@@ -17,6 +26,7 @@ import androidx.navigation.compose.composable
 import androidx.navigation.compose.rememberNavController
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.github.takahirom.roborazzi.RobolectricDeviceQualifiers
+import kotlinx.coroutines.awaitCancellation
 import org.junit.Assert.assertFalse
 import org.junit.Rule
 import org.junit.Test
@@ -38,8 +48,37 @@ class NowPlayingBackTest {
         composeRule.setContent {
             val nav = rememberNavController()
             navController = nav
+            val dispatcher = LocalOnBackPressedDispatcherOwner.current!!.onBackPressedDispatcher
+            val overlayBackCallback =
+                remember {
+                    object : OnBackPressedCallback(false) {
+                        override fun handleOnBackPressed() {
+                            overlayOpen = false
+                        }
+                    }
+                }
+            SideEffect { overlayBackCallback.isEnabled = overlayOpen }
             Box(Modifier.fillMaxSize()) {
-                NavHost(navController = nav, startDestination = "a") {
+                NavHost(
+                    navController = nav,
+                    startDestination = "a",
+                    enterTransition = {
+                        slideInHorizontally(initialOffsetX = { it / 4 }, animationSpec = tween(260)) +
+                            fadeIn(tween(260))
+                    },
+                    exitTransition = {
+                        slideOutHorizontally(targetOffsetX = { -it / 4 }, animationSpec = tween(260)) +
+                            fadeOut(tween(260))
+                    },
+                    popEnterTransition = {
+                        slideInHorizontally(initialOffsetX = { -it / 4 }, animationSpec = tween(260)) +
+                            fadeIn(tween(260))
+                    },
+                    popExitTransition = {
+                        slideOutHorizontally(targetOffsetX = { it / 4 }, animationSpec = tween(260)) +
+                            fadeOut(tween(260))
+                    },
+                ) {
                     composable("a") { Text("A") }
                     composable("b") { Text("B") }
                 }
@@ -47,10 +86,15 @@ class NowPlayingBackTest {
                     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
+            // The NavHost registers its back callback from a LaunchedEffect, so the overlay must
+            // register its own from a LaunchedEffect after it to land later in the dispatcher.
+            LaunchedEffect(dispatcher, overlayBackCallback) {
+                dispatcher.addCallback(overlayBackCallback)
+                try {
+                    awaitCancellation()
+                } finally {
+                    overlayBackCallback.remove()
+                }
             }
         }