fix(ui): opaque tab rows and bottom-bar under nav inset

When the disappearing bars translate on top of content, any translucent
chrome lets items bleed through — which the user noticed on Home: posts
became visible through the transparent SecondaryTabRow, and the strip
under Android's gesture bar (covered by windowInsetsPadding on the
bottom nav) was transparent too.

- Swap `containerColor = Color.Transparent` to
  `MaterialTheme.colorScheme.background` on all tab rows that sit in a
  DisappearingScaffold topBar slot (Home, Discover, Polls, Community,
  ChatroomListTabs, OldBookmarkList).
- Paint AppBottomBar's outer Column with the background before the
  windowInsetsPadding, so the system-gesture-bar strip at the bottom is
  opaque and items scrolling behind it are hidden.

FollowPackFeedScreen intentionally uses a translucent (alpha 0.6f) top
bar as a design choice, so it's left as-is.

https://claude.ai/code/session_01M3Bj24jLc9aVhMuvn55jXa

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/bottombars/AppBottomBar.kt

@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.ui.navigation.bottombars
 
 import androidx.compose.foundation.Canvas
+import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.RowScope
@@ -71,6 +72,7 @@ private fun RenderBottomMenu(
         modifier =
             Modifier
                 .fillMaxWidth()
+                .background(MaterialTheme.colorScheme.background)
                 .windowInsetsPadding(windowInsets)
                 .consumeWindowInsets(windowInsets)
                 .height(50.dp),

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/bookmarkgroups/old/OldBookmarkListScreen.kt

@@ -43,7 +43,6 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.platform.LocalContext
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.lifecycle.viewmodel.compose.viewModel
@@ -110,7 +109,7 @@ private fun RenderOldBookmarkScreen(
             Column {
                 TopBarWithBackButton(stringRes(id = R.string.old_bookmarks_title), nav::popBack)
                 SecondaryTabRow(
-                    containerColor = Color.Transparent,
+                    containerColor = MaterialTheme.colorScheme.background,
                     contentColor = MaterialTheme.colorScheme.onBackground,
                     selectedTabIndex = pagerState.currentPage,
                     modifier = TabRowHeight,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/rooms/feed/ChatroomListTabs.kt

@@ -46,7 +46,6 @@ import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.graphics.Color
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.ui.feeds.FeedContentState
 import com.vitorpamplona.amethyst.ui.components.M3ActionDialog
@@ -81,7 +80,7 @@ fun MessagesTabHeader(
 
     Box(Modifier.fillMaxWidth()) {
         SecondaryTabRow(
-            containerColor = Color.Transparent,
+            containerColor = MaterialTheme.colorScheme.background,
             contentColor = MaterialTheme.colorScheme.onBackground,
             selectedTabIndex = pagerState.currentPage,
             modifier = TabRowHeight,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/communities/CommunityScreen.kt

@@ -40,7 +40,6 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.vitorpamplona.amethyst.R
@@ -168,7 +167,7 @@ fun CommunityScreen(
             }
 
             SecondaryTabRow(
-                containerColor = Color.Transparent,
+                containerColor = MaterialTheme.colorScheme.background,
                 contentColor = MaterialTheme.colorScheme.onBackground,
                 modifier = TabRowHeight,
                 selectedTabIndex = pagerState.currentPage,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/discover/DiscoverScreen.kt

@@ -224,7 +224,7 @@ private fun DiscoverPages(
             Column {
                 DiscoveryTopBar(accountViewModel, nav)
                 SecondaryScrollableTabRow(
-                    containerColor = Color.Transparent,
+                    containerColor = MaterialTheme.colorScheme.background,
                     contentColor = MaterialTheme.colorScheme.onBackground,
                     selectedTabIndex = pagerState.currentPage,
                     modifier = TabRowHeight,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/home/HomeScreen.kt

@@ -53,7 +53,6 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.platform.LocalLayoutDirection
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
@@ -185,7 +184,7 @@ private fun HomePages(
             Column {
                 HomeTopBar(accountViewModel, nav)
                 SecondaryTabRow(
-                    containerColor = Color.Transparent,
+                    containerColor = MaterialTheme.colorScheme.background,
                     contentColor = MaterialTheme.colorScheme.onBackground,
                     modifier = TabRowHeight,
                     selectedTabIndex = pagerState.currentPage,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/polls/PollsScreen.kt

@@ -34,7 +34,6 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
-import androidx.compose.ui.graphics.Color
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.ui.feeds.FeedContentState
@@ -131,7 +130,7 @@ private fun PollsPages(
             Column {
                 PollsTopBar(accountViewModel, nav)
                 SecondaryTabRow(
-                    containerColor = Color.Transparent,
+                    containerColor = MaterialTheme.colorScheme.background,
                     contentColor = MaterialTheme.colorScheme.onBackground,
                     modifier = TabRowHeight,
                     selectedTabIndex = pagerState.currentPage,