Keep the split view mini player on pushed pages

The detail column absorbs its NavigationStack, so the mini player inset
on the stack only reached the root page and disappeared on push. Float
it over the split view, past the sidebar, and have every page reserve
its height as bottom safe area.

Yattee/Services/Navigation/NavigationDestination.swift

@@ -189,6 +189,7 @@ struct NavigationDestinationHandlerModifier: ViewModifier {
     func body(content: Content) -> some View {
         content
             .opaqueWindowBackground()
+            .miniPlayerBottomClearance()
             .navigationDestination(for: NavigationDestination.self) { destination in
                 Group {
                     if let transitionID = destination.transitionID {
@@ -199,10 +200,39 @@ struct NavigationDestinationHandlerModifier: ViewModifier {
                     }
                 }
                 .opaqueWindowBackground()
+                .miniPlayerBottomClearance()
             }
     }
 }
 
+extension EnvironmentValues {
+    /// Height of the split view's floating mini player, which every page in
+    /// the detail column reserves as bottom safe area. Zero elsewhere.
+    @Entry var miniPlayerBottomClearance: CGFloat = 0
+}
+
+/// Reserves the floating mini player's height at the bottom of a page.
+private struct MiniPlayerBottomClearanceModifier: ViewModifier {
+    @Environment(\.miniPlayerBottomClearance) private var clearance
+
+    func body(content: Content) -> some View {
+        #if os(iOS)
+        content
+            .safeAreaInset(edge: .bottom, spacing: 0) {
+                Color.clear.frame(height: clearance)
+            }
+        #else
+        content
+        #endif
+    }
+}
+
+private extension View {
+    func miniPlayerBottomClearance() -> some View {
+        modifier(MiniPlayerBottomClearanceModifier())
+    }
+}
+
 extension View {
     /// Adds navigation destination handlers for all app navigation destinations.
     /// Use this on views within a NavigationStack that contain NavigationLink(value:).