Section: repurpose SectionDivider() as explicit 2dp canvas-color line; use in Appearance themes card

SectionDivider() composable had 0 callsites and used Material Divider
with horizontal inset (unused legacy). Repurposed to draw a 2dp
canvas-color Box matching the auto-divider style used by
SectionItemView, gated by LocalInSectionCard so it no-ops outside a
section card.

Use it in Appearance themes card between WallpaperPresetSelector
(custom composable, not a SectionItemView, so no auto-divider) and the
following content (Remove image / Color mode / Dark mode), providing
the visual separator the user expects between the theme grid and the
rows below it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/helpers/Section.kt

@@ -311,9 +311,15 @@ fun SectionCustomFooter(padding: PaddingValues = PaddingValues(start = DEFAULT_P
   }
 }
 
+// Explicit 2dp canvas-color divider for inserting between non-SectionItemView
+// composables inside a SectionView card (e.g., between a custom block and a
+// SectionItemView). Auto-divider on SectionItemView handles the row-to-row
+// case; this one covers manual placement around mixed content. No-op outside
+// a SectionView card.
 @Composable
 fun SectionDivider() {
-  Divider(Modifier.padding(horizontal = 8.dp))
+  if (!LocalInSectionCard.current) return
+  Box(Modifier.fillMaxWidth().height(2.dp).background(canvasColorForCurrentTheme()))
 }
 
 @Composable

apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/usersettings/Appearance.kt

@@ -536,6 +536,7 @@ object AppearanceScope {
         },
         onChooseType = { onChooseType(it, importWallpaperLauncher) },
       )
+      SectionDivider()
       val type = MaterialTheme.wallpaper.type
       if (type is WallpaperType.Image && (themeUserDestination.value == null || perUserTheme.value.wallpaper?.imageFile != null)) {
         SectionItemView(disabled = chatModel.remoteHostId != null && themeUserDestination.value != null, click = {