refactor(ui): rework top bar nav as cockpit switch row (#697)

Replace the sliding accent pill and blurred underline with material-at-
rest tabs that speak the cyan identity language used elsewhere in the
chrome. Each tab is a full-height button with a tracked-mono uppercase
label, and the active tab carries a crisp 2px cyan rail flush with the
bar's bottom edge.

Drops the <Highlight> primitive, the springs import, and the unused
navTabValue memo/prop from EditorLayout.

frontend/src/components/EditorLayout.tsx

@@ -378,9 +378,6 @@ export default function EditorLayout() {
     return items;
   }, [isAdmin, isPaid, license?.variant, can]);
 
-  // Only highlight a tab if activeView matches a nav item
-  const navTabValue = navItems.some(i => i.value === activeView) ? activeView : undefined;
-
   // Reset editor state (extracted from Home button onClick)
   const resetEditorState = () => {
     setSelectedFile(null);
@@ -2484,7 +2481,6 @@ export default function EditorLayout() {
         <TopBar
           activeView={activeView}
           navItems={navItems}
-          navTabValue={navTabValue}
           onNavigate={handleNavigate}
           mobileNavOpen={mobileNavOpen}
           onMobileNavOpenChange={setMobileNavOpen}