feat: add terminal panel components and Zustand store for state management

- Created a barrel export file for terminal panel components.
- Implemented Zustand store for managing terminal panel UI state, including visibility, active terminal, view mode, and terminal ordering.
- Added actions for opening/closing the terminal panel, setting the active terminal, changing view modes, and managing terminal order.
- Introduced selectors for accessing terminal panel state properties.

ccw/frontend/src/components/layout/AppShell.tsx

@@ -127,10 +127,6 @@ export function AppShell({
     return () => window.removeEventListener('resize', handleResize);
   }, []);
 
-  const handleMenuClick = useCallback(() => {
-    setMobileOpen((prev) => !prev);
-  }, []);
-
   const handleMobileClose = useCallback(() => {
     setMobileOpen(false);
   }, []);

ccw/frontend/src/components/layout/Header.test.tsx

@@ -42,7 +42,7 @@ describe('Header Component - i18n Tests', () => {
 
   describe('translated aria-labels', () => {
     it('should have translated aria-label for menu toggle', () => {
-      render(<Header onMenuClick={vi.fn()} />);
+      render(<Header />);
 
       const menuButton = screen.getByRole('button', { name: /toggle navigation/i });
       expect(menuButton).toBeInTheDocument();