fix(desktop): theming + modifier review fixes from multi-agent analysis

Shapes:
- DeckSidebar: RoundedCornerShape(8.dp) → MaterialTheme.shapes.small
- NoteCard images: RoundedCornerShape(8.dp) → MaterialTheme.shapes.small

Modifier patterns:
- NoteCard: remove hardcoded .fillMaxWidth() — callers now pass it
- FeedScreen NoteCard callers: add explicit Modifier.fillMaxWidth()

Ripple clipping (from prior commit):
- SearchPill: clip(pill shape) before hoverHighlight()
- Sidebar items: clip before clickable
- ColumnHeader: padding before pointerInput

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/FeedScreen.kt

@@ -228,6 +228,7 @@ fun FeedNoteCard(
             val displayData = remember(originalEvent, metadataState) { originalEvent.toNoteDisplayData(localCache) }
             NoteCard(
                 note = displayData,
+                modifier = Modifier.fillMaxWidth(),
                 localCache = localCache,
                 onClick = { onNavigateToThread(originalEvent.id) },
                 onAuthorClick = onNavigateToProfile,
@@ -281,6 +282,7 @@ fun FeedNoteCard(
             val displayData = remember(event, metadataState) { event.toNoteDisplayData(localCache) }
             NoteCard(
                 note = displayData,
+                modifier = Modifier.fillMaxWidth(),
                 localCache = localCache,
                 onClick = { onNavigateToThread(event.id) },
                 onAuthorClick = onNavigateToProfile,

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/deck/DeckSidebar.kt

@@ -41,7 +41,6 @@ import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.shape.CircleShape
-import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.foundation.verticalScroll
 import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.MaterialTheme
@@ -416,7 +415,7 @@ private fun SidebarNavItem(
             Modifier
                 .fillMaxWidth()
                 .padding(horizontal = 8.dp, vertical = 2.dp)
-                .clip(RoundedCornerShape(8.dp))
+                .clip(MaterialTheme.shapes.small)
                 .clickable(onClick = onClick)
                 .background(backgroundColor)
                 .onPointerEvent(PointerEventType.Enter) { isHovered = true }
@@ -488,7 +487,7 @@ private fun SidebarFeedItem(
             Modifier
                 .fillMaxWidth()
                 .padding(horizontal = 8.dp, vertical = 2.dp)
-                .clip(RoundedCornerShape(8.dp))
+                .clip(MaterialTheme.shapes.small)
                 .clickable(onClick = onClick)
                 .background(backgroundColor)
                 .onPointerEvent(PointerEventType.Enter) { isHovered = true }

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/note/NoteCard.kt

@@ -237,7 +237,7 @@ fun NoteCard(
                             Modifier
                                 .fillMaxWidth()
                                 .heightIn(max = maxMediaHeight)
-                                .clip(RoundedCornerShape(8.dp))
+                                .clip(MaterialTheme.shapes.small)
                                 .then(
                                     if (onImageClick != null) {
                                         Modifier.clickable { onImageClick(imageUrls, index) }
@@ -311,7 +311,7 @@ fun NoteCard(
     if (onClick != null) {
         OutlinedCard(
             onClick = onClick,
-            modifier = modifier.fillMaxWidth(),
+            modifier = modifier,
             colors = cardColors,
             border = cardBorder,
             shape = cardShape,
@@ -319,7 +319,7 @@ fun NoteCard(
         )
     } else {
         OutlinedCard(
-            modifier = modifier.fillMaxWidth(),
+            modifier = modifier,
             colors = cardColors,
             border = cardBorder,
             shape = cardShape,