fix(android): re-assert Erkunden overlay back priority on every navigation

The root-level overlay back callback was keyed only on the overlay state, so after an
album drill-down or tab switch the NavHost could re-register its own back callback
above ours and regain priority — one back press then popped Erkunden → Home instead
of dismissing the overlay ("sometimes" bug). Key the DisposableEffect on
currentBackEntry as well, so the callback is removed and re-added (bumped to the top
of the OnBackPressedDispatcher) after every navigation while an overlay is open.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

android/app/src/main/kotlin/com/novasonic/app/ui/AppNavigation.kt

@@ -126,16 +126,6 @@ fun AppNavigation() {
         backDispatcher.addCallback(cb)
         onDispose { cb.remove() }
     }
-    DisposableEffect(exploreOverlayBack, backDispatcher) {
-        val action = exploreOverlayBack
-        if (action == null || backDispatcher == null) return@DisposableEffect onDispose {}
-        val cb = object : OnBackPressedCallback(true) {
-            override fun handleOnBackPressed() { action() }
-        }
-        backDispatcher.addCallback(cb)
-        onDispose { cb.remove() }
-    }
-
     fun coverUrl(coverId: String?) = repo.coverArtUrl(coverId, 600)
     fun heroCoverUrl(coverId: String?) = repo.coverArtUrl(coverId, 1000)
 
@@ -152,6 +142,20 @@ fun AppNavigation() {
     val currentRoute = currentBackEntry?.destination?.route
     val isTopLevel = TopLevel.entries.any { it.route == currentRoute }
 
+    // Root-level back for the Erkunden (Apple) overlay. Keyed on currentBackEntry as well, so the
+    // callback is re-added (bumped to the top of the OnBackPressedDispatcher) after every navigation
+    // — otherwise, once the NavHost re-registers its own callback during an album drill-down or tab
+    // switch, it could regain priority and pop Erkunden → Home on the next back ("sometimes" bug).
+    DisposableEffect(exploreOverlayBack, backDispatcher, currentBackEntry) {
+        val action = exploreOverlayBack
+        if (action == null || backDispatcher == null) return@DisposableEffect onDispose {}
+        val cb = object : OnBackPressedCallback(true) {
+            override fun handleOnBackPressed() { action() }
+        }
+        backDispatcher.addCallback(cb)
+        onDispose { cb.remove() }
+    }
+
     val bgGlow = Brush.radialGradient(
         colors = listOf(Color(0x0AE8A020), Color(0x00000000)),
         center = Offset.Unspecified, radius = 900f,