Fix double window-inset padding from the mini-player Scaffold hoist

Hoisting the mini-player into an outer Scaffold (previous commit)
introduced a real regression: extra space above the top header, and
a dead gap between the bottom tab bar and the mini-player.

Root cause: TopAppBar and Material3's NavigationBar (used by
BottomNavBar) are self-inset-aware - they only ever looked correct
because they sat directly at the true screen edges. Now they're
nested one level deeper inside the outer Scaffold's content area:
- The outer Scaffold has no topBar, so with its default
  contentWindowInsets it fell back to reserving the raw status-bar
  inset itself as top padding on the NavHost - on top of MainScreen's
  own TopAppBar doing the same thing a second time.
- BottomNavBar unconditionally pads itself for the navigation-bar
  inset regardless of what's below it, but MiniPlayerBar (which
  already self-pads for that inset) now always sits below it - so
  BottomNavBar was reserving space for an inset it's no longer
  adjacent to.

Fixed by zeroing contentWindowInsets on the outer Scaffold (it has
nothing of its own to protect beyond MiniPlayerBar's already-real
measured height) and zeroing BottomNavBar's own windowInsets (since
MiniPlayerBar is now what's genuinely bottom-adjacent).

Verified on-device across Home/Library/ArtistDetail/Settings: tight
header spacing restored, tab bar sits flush against the mini-player
with no gap.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/src/main/java/com/InfernalAquatics/deepwave/ui/components/BottomNavBar.kt

@@ -1,6 +1,7 @@
 package com.InfernalAquatics.deepwave.ui.components
 
 import android.content.res.Configuration
+import androidx.compose.foundation.layout.WindowInsets
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.Home
 import androidx.compose.material.icons.filled.LibraryMusic
@@ -28,7 +29,10 @@ enum class BottomTab(val labelRes: Int, val icon: ImageVector) {
 
 @Composable
 fun BottomNavBar(selectedTab: BottomTab, onTabSelected: (BottomTab) -> Unit) {
-    NavigationBar {
+    // Zero: MiniPlayerBar always sits below this now, so this is never actually the true
+    // bottom-most element - it would otherwise pad itself for a nav-bar inset that isn't
+    // adjacent to it anymore, leaving a dead gap above MiniPlayerBar.
+    NavigationBar(windowInsets = WindowInsets(0, 0, 0, 0)) {
         BottomTab.entries.forEach { tab ->
             val label = stringResource(tab.labelRes)
             NavigationBarItem(

app/src/main/java/com/InfernalAquatics/deepwave/ui/navigation/DeepwaveNavHost.kt

@@ -1,6 +1,7 @@
 package com.InfernalAquatics.deepwave.ui.navigation
 
 import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.WindowInsets
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.CircularProgressIndicator
@@ -52,6 +53,13 @@ fun DeepwaveNavHost(
             } ?: false
 
             Scaffold(
+                // Zero: this Scaffold has no topBar, and MiniPlayerBar already handles its own
+                // bottom nav-bar inset. Without this, Scaffold falls back to reserving the raw
+                // system-bar insets itself (since there's no topBar to "own" them), stacking on
+                // top of what each screen's own Scaffold below already does - double top padding,
+                // and a BottomNavBar that no longer sits at the true bottom edge padding for a
+                // nav-bar inset that isn't there anymore.
+                contentWindowInsets = WindowInsets(0, 0, 0, 0),
                 bottomBar = {
                     if (showMiniPlayer) {
                         MiniPlayerBar(