feat: add UI/UX polish with navigation rail, confirm dialogs, welcome banner, and form validation

- Add NavigationRail component (desktop vertical icon sidebar + mobile bottom tab bar)
- Add ConfirmDialog with promise-based useConfirmDialog hook for async confirmation flow
- Add WelcomeBanner onboarding component (one-time display, localStorage persistence)
- Polish login form UX (shake on error, TOTP slide animation, password visibility toggle, session expired banner)
- Add inline form validation with shake animation in email composer and contacts
- Add empty state patterns for contacts (no data vs no search results with contextual actions)
- Improve toast notification system with undo action support and typed durations
- Add WCAG AA prefers-reduced-motion media query, safe area insets, sr-only live regions
- Add template settings tab and keyboard shortcut integration
- Update all 8 locale translations

components/contacts/__tests__/contact-list.test.tsx

@@ -62,7 +62,7 @@ describe('ContactList', () => {
 
   it('shows empty state when no contacts match', () => {
     render(<ContactList {...defaultProps} contacts={[]} />);
-    expect(screen.getByText('empty_state')).toBeInTheDocument();
+    expect(screen.getByText('empty_state_title')).toBeInTheDocument();
   });
 
   it('shows search empty state when search has no results', () => {