fix(FN-700): remove duplicate mobile overflow menu buttons and clean up dead code

- Remove duplicate Terminal and Schedules buttons from mobile overflow menu in Header
- Remove unused CSS styles for mobile overflow menu items
- Clean up dead/duplicate route handler code in routes.ts
- Simplify TaskCard script button rendering logic
- Add tests for mobile Scripts button visibility in Header

packages/dashboard/app/components/Header.tsx

@@ -550,24 +550,6 @@ export function Header({
               <Clock size={16} />
               <span>Scheduled Tasks</span>
             </button>
-            <button
-              className="mobile-overflow-item"
-              onClick={() => handleOverflowAction(onToggleTerminal)}
-              role="menuitem"
-              data-testid="overflow-terminal-btn"
-            >
-              <Terminal size={16} />
-              <span>Open Terminal</span>
-            </button>
-            <button
-              className="mobile-overflow-item"
-              onClick={() => handleOverflowAction(onOpenSchedules)}
-              role="menuitem"
-              data-testid="overflow-schedules-btn"
-            >
-              <Clock size={16} />
-              <span>Scheduled Tasks</span>
-            </button>
             <button
               className="mobile-overflow-item"
               onClick={() => handleOverflowAction(onOpenSettings)}