feat(android): directional tab transitions in the bottom nav

Tab switches slid in a fixed direction (and sometimes flipped between push/pop feel,
so the direction felt random). Now the slide follows the target tab's position in the
bottom bar: tapping a tab to the right slides in from the right, a tab to the left
slides in from the left — applied across all four enter/exit/popEnter/popExit
transitions so it's consistent regardless of how Compose classifies the move. Detail
screen push/pop transitions are unchanged.

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

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

@@ -53,6 +53,10 @@ private enum class TopLevel(val route: String, val icon: ImageVector, val label:
 
 private val NavBg = Color(0xF7080814)
 
+// Position of a route among the top-level tabs (in bottom-bar order), or -1 if it isn't one.
+// Used to slide tab switches toward the side the target tab sits on, instead of a push/pop feel.
+private fun topLevelIndex(route: String?): Int = TopLevel.entries.indexOfFirst { it.route == route }
+
 @Composable
 fun AppNavigation() {
     val context = LocalContext.current
@@ -245,10 +249,36 @@ fun AppNavigation() {
                 navController    = navController,
                 startDestination = TopLevel.HOME.route,
                 modifier         = Modifier.padding(innerPadding),
-                enterTransition  = { slideInHorizontally(initialOffsetX = { it }, animationSpec = tween(280, easing = FastOutSlowInEasing)) + fadeIn(tween(200)) },
+                // Direction of a tab switch: +1 if the target tab sits to the right of the current
-                exitTransition   = { slideOutHorizontally(targetOffsetX = { -it / 3 }, animationSpec = tween(280, easing = FastOutSlowInEasing)) + fadeOut(tween(180)) },
+                // one, -1 if to the left, 0 if this isn't a tab-to-tab move (detail push/pop).
-                popEnterTransition = { slideInHorizontally(initialOffsetX = { -it / 3 }, animationSpec = tween(280, easing = FastOutSlowInEasing)) + fadeIn(tween(200)) },
+                enterTransition = {
-                popExitTransition = { slideOutHorizontally(targetOffsetX = { it }, animationSpec = tween(280, easing = FastOutSlowInEasing)) + fadeOut(tween(180)) },
+                    val f = topLevelIndex(initialState.destination.route)
+                    val t = topLevelIndex(targetState.destination.route)
+                    val dir = if (f >= 0 && t >= 0 && f != t) (if (t > f) 1 else -1) else 0
+                    if (dir != 0) slideInHorizontally(tween(280, easing = FastOutSlowInEasing)) { dir * it } + fadeIn(tween(200))
+                    else slideInHorizontally(tween(280, easing = FastOutSlowInEasing)) { it } + fadeIn(tween(200))
+                },
+                exitTransition = {
+                    val f = topLevelIndex(initialState.destination.route)
+                    val t = topLevelIndex(targetState.destination.route)
+                    val dir = if (f >= 0 && t >= 0 && f != t) (if (t > f) 1 else -1) else 0
+                    if (dir != 0) slideOutHorizontally(tween(280, easing = FastOutSlowInEasing)) { -dir * it } + fadeOut(tween(180))
+                    else slideOutHorizontally(tween(280, easing = FastOutSlowInEasing)) { -it / 3 } + fadeOut(tween(180))
+                },
+                popEnterTransition = {
+                    val f = topLevelIndex(initialState.destination.route)
+                    val t = topLevelIndex(targetState.destination.route)
+                    val dir = if (f >= 0 && t >= 0 && f != t) (if (t > f) 1 else -1) else 0
+                    if (dir != 0) slideInHorizontally(tween(280, easing = FastOutSlowInEasing)) { dir * it } + fadeIn(tween(200))
+                    else slideInHorizontally(tween(280, easing = FastOutSlowInEasing)) { -it / 3 } + fadeIn(tween(200))
+                },
+                popExitTransition = {
+                    val f = topLevelIndex(initialState.destination.route)
+                    val t = topLevelIndex(targetState.destination.route)
+                    val dir = if (f >= 0 && t >= 0 && f != t) (if (t > f) 1 else -1) else 0
+                    if (dir != 0) slideOutHorizontally(tween(280, easing = FastOutSlowInEasing)) { -dir * it } + fadeOut(tween(180))
+                    else slideOutHorizontally(tween(280, easing = FastOutSlowInEasing)) { it } + fadeOut(tween(180))
+                },
             ) {
                 composable(TopLevel.HOME.route) {
                     HomeScreen(