fix(nests): NestChatPanel takes weight(1) so chat fills the screen

Previously the room screen wrapped EVERYTHING — title, summary,
participants, talk row, action row, AND chat — in a single
verticalScroll Column. The chat panel sat at the bottom with a fixed
NEST_CHAT_PANEL_HEIGHT (420dp), which meant on tall phones the chat
left blank space below it and on small phones the chat was cramped.

Restructure NestFullScreen's body:
  - Outer Column.fillMaxSize, no scroll, owns safeDrawing inset.
  - Top metadata: Column with weight(1f, fill=false), internal
    verticalScroll, horizontal+top padding. Caps at half the screen
    so an over-tall participants list scrolls internally instead of
    pushing the chat off-screen.
  - NestChatPanel: Column-scoped weight(1f, fill=true), horizontal
    padding + bottom inset. Always takes its full allocation —
    chat dominates the screen, fixed-height fallback gone.

NestChatPanel is now a `ColumnScope.NestChatPanel` extension so its
modifier can use `weight()` from the caller. Inside the panel, the
message list Box also uses weight(1f, fill=true) of the panel's own
Column, so the LazyColumn fills everything except the composer.

NEST_CHAT_PANEL_HEIGHT constant removed — it was the source of the
fixed-height behavior the user explicitly didn't want.

https://claude.ai/code/session_01RDpuki4t8StSg1CZcXnV5b

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/nests/room/NestChatPanel.kt

@@ -22,6 +22,7 @@ package com.vitorpamplona.amethyst.ui.screen.loggedIn.nests.room
 
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.ColumnScope
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
@@ -97,7 +98,7 @@ import kotlinx.coroutines.launch
  * which are pinned to the channel-VM model — out of scope here.
  */
 @Composable
-internal fun NestChatPanel(
+internal fun ColumnScope.NestChatPanel(
     event: MeetingSpaceEvent,
     viewModel: NestViewModel,
     accountViewModel: AccountViewModel,
@@ -120,7 +121,7 @@ internal fun NestChatPanel(
     val routeForLastRead = remember(event) { "NestChat/${event.address().toValue()}" }
 
     Column(modifier = modifier.fillMaxWidth()) {
-        Box(modifier = Modifier.fillMaxWidth().height(NEST_CHAT_PANEL_HEIGHT)) {
+        Box(modifier = Modifier.fillMaxWidth().weight(1f, fill = true)) {
             if (messages.isEmpty()) {
                 Text(
                     text = stringRes(R.string.nest_chat_empty),
@@ -266,6 +267,4 @@ private fun NestChatComposer(
     }
 }
 
-private val NEST_CHAT_PANEL_HEIGHT = 420.dp
-
 private val NEST_CHAT_NO_OP_NOTE: (com.vitorpamplona.amethyst.model.Note) -> Unit = {}

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/nests/room/NestFullScreen.kt

@@ -98,19 +98,20 @@ internal fun NestFullScreen(
 ) {
     val roomTheme = androidx.compose.runtime.remember(event) { RoomTheme.from(event) }
     NestThemedScope(theme = roomTheme, accountViewModel = accountViewModel) {
-        // Inset the room content inside the system bars so the title
-        // doesn't slide under the status bar and the Leave / chat
-        // composer don't sit beneath the gesture / nav bar. The
-        // themed background color and `bg` image still paint
-        // edge-to-edge — they live on NestThemedScope's outer Box,
-        // which is intentionally outside this padding.
+        // Outer column owns the safeDrawing inset; the top metadata
+        // section and the chat panel are weighted siblings.
+        //
+        // The top section uses `weight(1f, fill = false)` so it never
+        // exceeds half the screen and scrolls internally if it would.
+        // The chat uses `weight(1f, fill = true)` so it always takes
+        // its full allocation — the user explicitly wanted chat to
+        // dominate the screen rather than ride a fixed-height box at
+        // the bottom of the metadata scroll.
         Column(
             modifier =
                 Modifier
                     .fillMaxSize()
-                    .windowInsetsPadding(WindowInsets.safeDrawing)
-                    .padding(16.dp)
-                    .verticalScroll(rememberScrollState()),
+                    .windowInsetsPadding(WindowInsets.safeDrawing),
         ) {
             var showEditSheet by rememberSaveable { mutableStateOf(false) }
             var showHostMenu by rememberSaveable { mutableStateOf(false) }
@@ -118,6 +119,14 @@ internal fun NestFullScreen(
             val isHost = accountViewModel.account.signer.pubKey == event.pubKey
             val leaveScope = rememberCoroutineScope()
 
+            Column(
+                modifier =
+                    Modifier
+                        .weight(1f, fill = false)
+                        .verticalScroll(rememberScrollState())
+                        .padding(horizontal = 16.dp)
+                        .padding(top = 16.dp),
+            ) {
                 Row(
                     modifier = Modifier.fillMaxWidth(),
                     horizontalArrangement = Arrangement.SpaceBetween,
@@ -332,12 +341,17 @@ internal fun NestFullScreen(
                         },
                     )
                 }
+            }
 
             NestChatPanel(
                 event = event,
                 viewModel = viewModel,
                 accountViewModel = accountViewModel,
-                modifier = Modifier.padding(top = 12.dp),
+                modifier =
+                    Modifier
+                        .weight(1f, fill = true)
+                        .padding(horizontal = 16.dp)
+                        .padding(top = 12.dp, bottom = 16.dp),
             )
         }
     }