revert(navbar): remove bottom fade gradient

Removed the 10px gradient fade at the bottom of the navbar per user request.
Kept the border fix that removes the black line artifact when transparent.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/components/AppNavBar.tsx

@@ -575,12 +575,8 @@ export function AppNavBar({ variant = 'full', navSlot }: AppNavBarProps) {
   return (
     <Tooltip.Provider delayDuration={200}>
       <header
-        style={{
-          background: isTransparent
-            ? 'transparent'
-            : 'linear-gradient(180deg, rgba(0, 0, 0, 0.5) 0%, rgba(0, 0, 0, 0.5) calc(100% - 10px), transparent 100%)',
-        }}
         className={css({
+          bg: isTransparent ? 'transparent' : 'rgba(0, 0, 0, 0.5)',
           backdropFilter: isTransparent ? 'none' : 'blur(12px)',
           shadow: isTransparent ? 'none' : 'lg',
           borderBottom: isTransparent ? 'none' : '1px solid',