fix desktop canvas header blur in split channel management (#1558)

Signed-off-by: Taylor Ho <taylorkmho@gmail.com>
Co-authored-by: npub1223z34hd7vtwc6qj4s7flsxkj644nlre2nthu7lrrmkumhu3xddsrx9r6w <52a228d6edf316ec6812ac3c9fc0d696ab59fc7954d77e7be31eedcddf91335b@sprout-oss.stage.blox.sqprod.co>

desktop/src/features/channels/ui/ChannelManagementSheet.tsx

@@ -353,14 +353,15 @@ export function ChannelManagementSheet({
         </DialogPrimitive.Portal>
       ) : null}
       {isSplitLayout ? (
+        // No translucent backdrop-blur surface here: `backdrop-filter`
+        // creates a stacking context that traps the z-40 panel header below
+        // the shared z-30 header blur strip in split layout. The pane sits on
+        // the opaque `bg-background` from PANEL_BASE_CLASS instead.
         <DialogPrimitive.Content
           className={cn(
             PANEL_BASE_CLASS,
             "h-full w-full cursor-default overflow-hidden border-l-0 p-0",
             animateSplitEnter && PANEL_ENTER_MOTION_CLASS,
-            isDark
-              ? "bg-background/85 backdrop-blur-xl supports-backdrop-filter:bg-background/75"
-              : "bg-background",
           )}
           data-testid="channel-management-sheet"
           onEscapeKeyDown={(event) => event.preventDefault()}