fix(desktop): hover-state polish + Search width cap + reserve reaction-icon space

NoteCard hover (header+text inner clickable + avatar/name chip):
- Clip(RoundedCornerShape(8.dp)) before .clickable on the header+text
  Column so the ripple rounds instead of cutting a hard rectangle.
- Avatar+name chip gets a stadium clip (RoundedCornerShape(100.dp))
  before its clickable — matches how Slack / Notion / Linear render
  user-pill hover states.

Chat bubble hover (ChatBubbleLayout):
- combinedClickable was applied outside the Surface's shape clipping,
  so the ripple ignored ChatBubbleShapeMe/Them. Moved the shape into a
  named val and added Modifier.clip(bubbleShape) ahead of
  combinedClickable. Hover now rounds with the bubble.

Chat reaction icon (ChatPane detailRow):
- On hover the "add reaction" icon used to conditionally appear and
  shift every other element in the detail row, causing the whole list
  to reflow up or down. Wrapped in a Box with Modifier.alpha that
  fades in/out — the icon is always laid out so the row stays fixed.
  Button is disabled when not hovered so it's click-through when
  invisible.

Search text field:
- Now padded by LocalReadingSidePadding so it stays inside the 720dp
  reading column on wide displays (previously the search Row's
  fillMaxWidth spanned the whole window after the ReadingColumn
  refactor).
- Bumped height from 40dp → 44dp. M3 OutlinedTextField has ~16dp of
  internal vertical content padding that was clipping the bodyMedium
  placeholder at 40dp. Same change for the chat input.

https://claude.ai/code/session_01NufduPfZvYQVYwLkbCjCUo

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/chat/ChatBubbleLayout.kt

@@ -34,6 +34,7 @@ import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.compositeOver
 import com.vitorpamplona.amethyst.commons.ui.theme.ChatBubbleMaxSizeModifier
@@ -128,18 +129,23 @@ fun ChatBubbleLayout(
                 )
             }
 
+        val bubbleShape = if (isLoggedInUser) ChatBubbleShapeMe else ChatBubbleShapeThem
+        // Clip the hover/ripple to the bubble shape — combinedClickable otherwise
+        // paints a rectangular ripple that ignores the Surface's rounded corners.
         val clickableModifier =
-            remember {
-                Modifier.combinedClickable(
-                    onClick = {
-                        if (!onClick()) {
-                            if (!isComplete) {
-                                showDetails.value = !showDetails.value
+            remember(bubbleShape) {
+                Modifier
+                    .clip(bubbleShape)
+                    .combinedClickable(
+                        onClick = {
+                            if (!onClick()) {
+                                if (!isComplete) {
+                                    showDetails.value = !showDetails.value
+                                }
                             }
-                        }
-                    },
-                    onLongClick = { popupExpanded.value = true },
-                )
+                        },
+                        onLongClick = { popupExpanded.value = true },
+                    )
             }
 
         Row(
@@ -148,7 +154,7 @@ fun ChatBubbleLayout(
         ) {
             Surface(
                 color = bgColor.value,
-                shape = if (isLoggedInUser) ChatBubbleShapeMe else ChatBubbleShapeThem,
+                shape = bubbleShape,
                 modifier = clickableModifier,
             ) {
                 Column(modifier = MessageBubbleLimits, verticalArrangement = ChatRowColSpacing5dp) {