loading: shimmer placeholders on every list screen

The placeholders only existed on the home rows; the shared list screens
(My videos, Search, Subscriptions, History, channel pages) still used a
full-screen spinner, and the Channels screen did too. All of them now
show card-shaped placeholders: the in-grid initial pass keeps the page
header and a two-row placeholder block, growing lists swap the always-
visible bottom spinner chip for a placeholder row driven by the new
loadingMore state on PagedListViewModel, and the channels screen shows
stub header bars plus placeholder rows while it starts up.

Closes #19

app/src/main/java/net/jeena/jtubetv/ui/list/PagedListViewModel.kt

@@ -25,6 +25,10 @@ abstract class PagedListViewModel<T> : ViewModel() {
     var loadingInitial by mutableStateOf(true)
         private set
 
+    /** True while a follow-up page is being fetched — UI shows placeholders ( issue #19). */
+    var loadingMore by mutableStateOf(false)
+        private set
+
     /**
      * Show an instant (possibly stale) snapshot before the network load lands
      * (issue #9): no spinner, content paints immediately and [refresh]-style
@@ -57,6 +61,7 @@ abstract class PagedListViewModel<T> : ViewModel() {
     fun loadMore(force: Boolean = false) {
         if (inFlight || (!force && exhausted)) return
         inFlight = true
+        loadingMore = !force // the initial kick is a fresh list, not a "load more"
         initialError = null
         viewModelScope.launch {
             try {
@@ -78,6 +83,7 @@ abstract class PagedListViewModel<T> : ViewModel() {
                 )
             } finally {
                 inFlight = false
+                loadingMore = false
             }
         }
     }

app/src/main/java/net/jeena/jtubetv/ui/screens/ChannelsScreen.kt

@@ -13,6 +13,7 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.LazyRow
@@ -340,9 +341,23 @@ fun ChannelsScreen(
 
 
     when {
-        viewModel.loading && viewModel.userRows.isEmpty() -> Box(
-            Modifier.fillMaxSize(), contentAlignment = Alignment.Center,
-        ) { androidx.compose.material3.CircularProgressIndicator() }
+        viewModel.loading && viewModel.userRows.isEmpty() ->
+            // Placeholder rows while the channels load (issue #19): header stub
+            // + a row of shimmer card-shaped placeholders, twice.
+            androidx.compose.foundation.layout.Column {
+                repeat(2) {
+                    Box(Modifier.padding(start = 16.dp, top = 12.dp, bottom = 4.dp)) {
+                        Box(
+                            Modifier
+                                .width(180.dp)
+                                .height(22.dp)
+                                .clip(CircleShape)
+                                .background(Color(0xFF232323)),
+                        )
+                    }
+                    ShimmerRow()
+                }
+            }
         viewModel.error != null && viewModel.userRows.isEmpty() ->
             Box(Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
                 Column(horizontalAlignment = Alignment.CenterHorizontally) {

app/src/main/java/net/jeena/jtubetv/ui/screens/HomeRows.kt

@@ -41,6 +41,7 @@ import net.jeena.jtubetv.data.PeerTubeRepository
 import net.jeena.jtubetv.data.api.VideoDto
 import net.jeena.jtubetv.ui.list.PagedListViewModel
 import net.jeena.jtubetv.ui.list.Snapshots
+import net.jeena.jtubetv.ui.screens.list.ShimmerCard
 import net.jeena.jtubetv.ui.screens.list.VideoCard
 
 /** Compact SmartTube-style card: ~4 and a bit visible per full-width row. */
@@ -407,12 +408,10 @@ fun HomeRowsScreen(
 
 /** Placeholder row of dummy cards (issue #19). */
 @Composable
-private fun ShimmerRow(size: Int = 4) {
+fun ShimmerRow(size: Int = 4) {
     Row(Modifier.padding(horizontal = 12.dp)) {
-        androidx.compose.foundation.layout.Row {
-        }
         repeat(size) {
-            net.jeena.jtubetv.ui.screens.list.ShimmerCard(
+            ShimmerCard(
                 modifier = Modifier
                     .padding(horizontal = 4.dp)
                     .width(rowCardWidth()),

app/src/main/java/net/jeena/jtubetv/ui/screens/list/VideoListScreen.kt

@@ -10,6 +10,7 @@ import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.lazy.grid.GridCells
@@ -117,13 +118,7 @@ fun VideoListScreen(
         }
     }
 
-    if (viewModel.loadingInitial && items.isEmpty()) {
-        Box(Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
-            CircularProgressIndicator()
-        }
-        LaunchedEffect(source) { viewModel.loadMore(force = true) }
-        return
-    }
+
 
     if (items.isEmpty()) {
         Box(
@@ -171,6 +166,30 @@ fun VideoListScreen(
                 else -> {}
             }
         }
+        if (items.isEmpty() && viewModel.loadingInitial) {
+            // Placeholder cards while the page's first chunk loads (issue #19):
+            // shaped like the real cards, with the faint shimmer, on every
+            // VideoListScreen (My videos, Search, Subscriptions, History, channel pages).
+            item(key = "initial-placeholders", span = { androidx.compose.foundation.lazy.grid.GridItemSpan(maxLineSpan) }) {
+                LaunchedEffect(source) { viewModel.loadMore(force = true) }
+                androidx.compose.foundation.layout.Column {
+                    repeat(2) {
+                        androidx.compose.foundation.layout.Row {
+                            repeat(cardsPerRow) {
+                                ShimmerCard(
+                                    modifier = Modifier
+                                        .padding(6.dp)
+                                        .width(rowCardWidth()),
+                                )
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        if (items.isEmpty() && !viewModel.loadingInitial && viewModel.initialError == null) {
+            return@LazyVerticalGrid
+        }
         itemsIndexed(items, key = { _, item -> itemStableKey(item) }) { index, item ->
             val video: VideoDto = when (item) {
                 is VideoListItem.HistoryEntry -> item.history.video
@@ -193,10 +212,18 @@ fun VideoListScreen(
                 LaunchedEffect(index) { viewModel.loadMore() }
             }
         }
-        if (!viewModel.exhausted) {
-            item {
-                Box(Modifier.fillMaxWidth().padding(24.dp), contentAlignment = Alignment.Center) {
-                    CircularProgressIndicator()
+        if (viewModel.loadingMore) {
+            // Growing the list: placeholder row (issue #19) instead of the
+            // permanent spinner chip that used to sit under every list.
+            item(key = "load-more-placeholders") {
+                androidx.compose.foundation.layout.Row {
+                    repeat(cardsPerRow) {
+                        ShimmerCard(
+                            modifier = Modifier
+                                .padding(6.dp)
+                                .width(rowCardWidth()),
+                        )
+                    }
                 }
             }
         }