fix(app): hide branch icon on non-git workspace headers

Gate the GitBranch icon behind isGitCheckout, and keep the header
skeleton visible until the checkout status query resolves so the icon
doesn't pop in and cause layout shift.

packages/app/src/components/branch-switcher.tsx

@@ -45,7 +45,7 @@ export function BranchSwitcher({
 
   const titleContent = (
     <>
-      <GitBranch size={14} color={theme.colors.foregroundMuted} />
+      {isGitCheckout ? <GitBranch size={14} color={theme.colors.foregroundMuted} /> : null}
       <Text testID="workspace-header-title" style={styles.headerTitle} numberOfLines={1}>
         {title}
       </Text>