ui(navigation): standardize bar styling and enhance item selection visuals

Remove custom floating card styling, dynamic window inset padding, and
clipping modifiers from the bottom NavigationBar to restore standard
layout behavior. Remove the explicit zeroed window insets from the
NavigationRail as well.

Reduce the opacity of the selected indicator color to 60% on both
NavigationBarItem and NavigationRailItem components.

Update NavigationBarItem labels to use bold font weight when selected.

Author: CodePandaaAI

shared/src/commonMain/kotlin/com/liftley/sync360/Sync360Root.kt

@@ -1,21 +1,20 @@
 package com.liftley.sync360
 
 import androidx.compose.foundation.layout.Row
-import androidx.compose.foundation.layout.WindowInsets
 import androidx.compose.foundation.layout.consumeWindowInsets
 import androidx.compose.foundation.layout.fillMaxHeight
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.padding
-import androidx.compose.foundation.layout.windowInsetsPadding
 import androidx.compose.material3.CenterAlignedTopAppBar
 import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
 import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.NavigationBar
-import androidx.compose.material3.NavigationBarDefaults
 import androidx.compose.material3.NavigationBarItem
+import androidx.compose.material3.NavigationBarItemDefaults
 import androidx.compose.material3.NavigationRail
 import androidx.compose.material3.NavigationRailItem
+import androidx.compose.material3.NavigationRailItemDefaults
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Text
 import androidx.compose.material3.TopAppBarDefaults
@@ -25,8 +24,8 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.draw.clip
 import androidx.compose.ui.keepScreenOn
+import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
@@ -86,26 +85,34 @@ fun Sync360Root() {
         is SendState.Failed -> "Could Not Send"
     }
 
+    val navigationBarColorWhenSelected = NavigationBarItemDefaults.colors().copy(
+        selectedIndicatorColor = MaterialTheme.colorScheme.secondaryContainer.copy(
+            alpha = 0.6f
+        )
+    )
+
+    val navigationRailColorWhenSelected = NavigationRailItemDefaults.colors().copy(
+        selectedIndicatorColor = MaterialTheme.colorScheme.secondaryContainer.copy(
+            alpha = 0.6f
+        )
+    )
+
     Scaffold(
         bottomBar = {
             if (!useNavigationRail) {
-                NavigationBar(
-                    modifier = Modifier
-                        // 1. Fetch system bar insets dynamically to protect the Android gesture area
-                        .windowInsetsPadding(NavigationBarDefaults.windowInsets)
-                        // 2. Add outer floating padding around the bar (converted from dp)
-                        .padding(horizontal = 32.dp, vertical = 16.dp)
-                        // 3. Clip the corners after padding to create the floating card shape
-                        .clip(MaterialTheme.shapes.extraExtraLarge),
-                    containerColor = MaterialTheme.colorScheme.surface,
-                    // 4. Disable internal inset consumption so our custom modifiers control the shape
-                    windowInsets = WindowInsets(0, 0, 0, 0)
-                ) {
+                NavigationBar(containerColor = MaterialTheme.colorScheme.surface) {
                     NavigationBarItem(
+                        colors = navigationBarColorWhenSelected,
                         onClick = { navigationViewModel.navigateTo(NavScreen.ReceiveScreen) },
                         selected = navigationViewModel.currentScreen() ==
                                 NavScreen.ReceiveScreen,
-                        label = { Text("Receive") },
+                        label = {
+                            Text(
+                                "Receive", fontWeight = if (navigationViewModel.currentScreen() ==
+                                    NavScreen.ReceiveScreen
+                                ) FontWeight.Bold else FontWeight.Normal
+                            )
+                        },
                         icon = {
                             Icon(
                                 imageVector = Download,
@@ -114,10 +121,17 @@ fun Sync360Root() {
                         }
                     )
                     NavigationBarItem(
+                        colors = navigationBarColorWhenSelected,
                         onClick = { navigationViewModel.navigateTo(NavScreen.SendScreen) },
                         selected = navigationViewModel.currentScreen() ==
                                 NavScreen.SendScreen,
-                        label = { Text("Send") },
+                        label = {
+                            Text(
+                                "Send", fontWeight = if (navigationViewModel.currentScreen() ==
+                                    NavScreen.SendScreen
+                                ) FontWeight.Bold else FontWeight.Normal
+                            )
+                        },
                         icon = {
                             Icon(
                                 imageVector = Send,
@@ -164,11 +178,10 @@ fun Sync360Root() {
             if (useNavigationRail) {
                 NavigationRail(
                     modifier = Modifier.fillMaxHeight(),
-                    containerColor = MaterialTheme.colorScheme.surfaceContainer,
-                    // Scaffold has already supplied the system-bar padding.
-                    windowInsets = WindowInsets(0, 0, 0, 0)
+                    containerColor = MaterialTheme.colorScheme.surfaceContainer
                 ) {
                     NavigationRailItem(
+                        colors = navigationRailColorWhenSelected,
                         selected = currentScreen == NavScreen.ReceiveScreen,
                         onClick = { navigationViewModel.navigateTo(NavScreen.ReceiveScreen) },
                         icon = {
@@ -181,6 +194,7 @@ fun Sync360Root() {
                     )
 
                     NavigationRailItem(
+                        colors = navigationRailColorWhenSelected,
                         selected = currentScreen == NavScreen.SendScreen,
                         onClick = { navigationViewModel.navigateTo(NavScreen.SendScreen) },
                         icon = {