android: shrink composer pill; float it over the message list

- reduce composer size (padding, corner radius, send button 40->36dp)
- move composer plane (back-to-bottom button, attachments, banners,
  slash drawer, input pill) into a bottom overlay so messages scroll
  behind it; overlay height drives the list's bottom content padding

app/shared/src/commonMain/kotlin/iris/ui/screens/ChatScreen.kt

@@ -69,6 +69,7 @@ import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
@@ -91,6 +92,7 @@ import androidx.compose.ui.input.key.key
 import androidx.compose.ui.input.key.onPreviewKeyEvent
 import androidx.compose.ui.input.key.type
 import androidx.compose.ui.layout.ContentScale
+import androidx.compose.ui.layout.onSizeChanged
 import androidx.compose.ui.platform.LocalClipboardManager
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.platform.LocalFocusManager
@@ -474,14 +476,26 @@ fun ChatScreen(controller: IrisController) {
                 )
             }
 
-            // Messages (M7: interleaved date separators; bubbles capped at 85% width)
+            // Messages (M7: interleaved date separators; bubbles capped at 85% width).
+            // The composer plane (back-to-bottom button, attachments, banners, slash
+            // drawer, input pill) is an OVERLAY at the bottom of this area: the list
+            // scrolls behind it, so the pill floats over the wallpaper instead of
+            // sitting in a hard-edged gap. The overlay's measured height becomes the
+            // list's bottom content padding, keeping the newest message visible above it.
+            var overlayHeightPx by remember { mutableIntStateOf(0) }
             val rows = remember(items) { buildChatRows(items) }
             BoxWithConstraints(modifier = Modifier.weight(1f).fillMaxWidth()) {
                 val bubbleMaxWidth = (maxWidth.value * 0.85f).dp
                 LazyColumn(
                     state = listState,
                     modifier = Modifier.fillMaxSize(),
-                    contentPadding = PaddingValues(16.dp),
+                    contentPadding =
+                        PaddingValues(
+                            start = 16.dp,
+                            top = 16.dp,
+                            end = 16.dp,
+                            bottom = (overlayHeightPx / LocalDensity.current.density).dp + 16.dp,
+                        ),
                     verticalArrangement = Arrangement.spacedBy(8.dp),
                 ) {
                     if (items.isEmpty() && !typing) {
@@ -552,17 +566,27 @@ fun ChatScreen(controller: IrisController) {
                     }
                 }
 
+                // Composer plane (overlay): back-to-bottom button, attachments, banners,
+                // slash drawer and the input pill. The list scrolls behind it; its
+                // measured height is the list's bottom content padding (above).
+                Column(
+                    modifier =
+                        Modifier
+                            .align(Alignment.BottomCenter)
+                            .fillMaxWidth()
+                            .onSizeChanged { overlayHeightPx = it.height },
+                ) {
                     // Back-to-bottom button: appears once the user has scrolled up
                     // to read history; a tap glides the view back to the latest
                     // message (smooth but quick).
                     if (!isAtBottom && !isAutoScrolling) {
+                        Box(modifier = Modifier.fillMaxWidth(), contentAlignment = Alignment.CenterEnd) {
                             val alpha = remember { Animatable(0f) }
                             LaunchedEffect(Unit) { alpha.animateTo(1f, tween(150)) }
                             Box(
                                 modifier =
                                     Modifier
-                                .align(Alignment.BottomEnd)
+                                        .padding(end = 16.dp, bottom = 8.dp)
-                                .padding(end = 16.dp, bottom = 12.dp)
                                         .alpha(alpha.value)
                                         .size(40.dp)
                                         .clip(CircleShape)
@@ -777,17 +801,17 @@ fun ChatScreen(controller: IrisController) {
                             modifier =
                                 Modifier
                                     .fillMaxWidth()
-                            .padding(horizontal = 12.dp, vertical = 8.dp)
+                                    .padding(horizontal = 12.dp, vertical = 6.dp)
-                            .clip(RoundedCornerShape(28.dp))
+                                    .clip(RoundedCornerShape(24.dp))
                                     .background(IrisColors.surface)
-                            .padding(horizontal = 6.dp, vertical = 4.dp),
+                                    .padding(horizontal = 6.dp, vertical = 2.dp),
                             verticalAlignment = Alignment.CenterVertically,
                         ) {
                             Row(
                                 modifier =
                                     Modifier
                                         .weight(1f)
-                                .padding(horizontal = 6.dp, vertical = 10.dp),
+                                        .padding(horizontal = 6.dp, vertical = 6.dp),
                                 verticalAlignment = Alignment.CenterVertically,
                             ) {
                                 Box(modifier = Modifier.weight(1f)) {
@@ -797,8 +821,16 @@ fun ChatScreen(controller: IrisController) {
                                         modifier =
                                             Modifier
                                                 .fillMaxWidth()
-                                        .heightIn(max = if (textHeightPx > 0f) (textHeightPx / layoutDensity).dp else Dp.Unspecified)
+                                                .heightIn(
-                                        .focusRequester(composerFocusRequester)
+                                                    max =
+                                                        if (textHeightPx >
+                                                            0f
+                                                        ) {
+                                                            (textHeightPx / layoutDensity).dp
+                                                        } else {
+                                                            Dp.Unspecified
+                                                        },
+                                                ).focusRequester(composerFocusRequester)
                                                 .onFocusChanged { composerFocused = it.isFocused },
                                         textStyle = MaterialTheme.typography.bodyLarge.copy(color = IrisColors.onSurface),
                                         keyboardOptions = KeyboardOptions(imeAction = ImeAction.Send),
@@ -827,13 +859,15 @@ fun ChatScreen(controller: IrisController) {
                             Box(
                                 modifier =
                                     Modifier
-                                .size(40.dp)
+                                        .size(36.dp)
                                         .clip(CircleShape)
                                         .background(if (canSend) IrisColors.primary else IrisColors.primary.copy(alpha = 0.35f))
                                         .clickable(enabled = canSend) { doSend() },
                                 contentAlignment = Alignment.Center,
                             ) {
-                        Text("➤", color = Color.White, fontSize = 16.sp)
+                                Text("➤", color = Color.White, fontSize = 14.sp)
+                            }
+                        }
                     }
                 }
             }