fix(desktop): carve sidebar nav rows out of the titlebar drag region (#44453)

A WSL2 user reported the top two left-sidebar items being unclickable
while the rest of the UI works. That symptom shape matches an
-webkit-app-region:drag hit-test band eating clicks, not GPU/compositing:
the shell's titlebar drag strips (app-shell.tsx) span the top 34px and
the nav group clears them by only 6px, and drag regions win hit-testing
over DOM regardless of pointer-events. Linux WCO (Electron >=32) is the
newest implementation and has known region quirks (electron#43030).

Apply the same no-drag carve-out the codebase already uses for sticky
user bubbles (USER_BUBBLE_BASE_CLASS in thread.tsx) to the sidebar nav
buttons. Harmless on every platform: the rows were never meant to be
draggable surface.

apps/desktop/src/app/chat/sidebar/index.tsx

@@ -797,7 +797,14 @@ export function ChatSidebar({
                     <SidebarMenuButton
                       aria-disabled={!isInteractive}
                       className={cn(
-                        'flex h-7 w-full justify-start gap-2 rounded-md border border-transparent px-2 text-left text-[0.8125rem] font-medium text-(--ui-text-secondary) transition-colors duration-100 ease-out hover:bg-(--ui-control-hover-background) hover:text-foreground hover:transition-none',
+                        // no-drag: these rows sit directly under the titlebar's
+                        // [-webkit-app-region:drag] strips (app-shell.tsx), with only
+                        // 6px of clearance. Drag regions win hit-testing over DOM
+                        // (pointer-events can't override), and on Linux/WSLg the
+                        // resolved region has been observed to swallow clicks on the
+                        // top rows. Same carve-out as USER_BUBBLE_BASE_CLASS in
+                        // thread.tsx.
+                        'flex h-7 w-full justify-start gap-2 rounded-md border border-transparent px-2 text-left text-[0.8125rem] font-medium text-(--ui-text-secondary) transition-colors duration-100 ease-out [-webkit-app-region:no-drag] hover:bg-(--ui-control-hover-background) hover:text-foreground hover:transition-none',
                         active &&
                           'border-(--ui-stroke-tertiary) bg-(--ui-control-active-background) text-foreground shadow-none hover:border-(--ui-stroke-tertiary)!',
                         !isInteractive &&