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

app/globals.css

@@ -296,6 +296,7 @@ body {
   animation: slide-in 0.3s ease-out;
 }
 
+
 /* Mobile Responsive Utilities */
 
 /* Safe area insets for notched devices (iPhone X+, etc.) */
@@ -385,3 +386,23 @@ body {
 .animate-slide-in-from-left {
   animation: slide-in-from-left 0.3s ease-out;
 }
+
+/* Reduced motion: respect user OS preference */
+@media (prefers-reduced-motion: reduce) {
+  *,
+  *::before,
+  *::after {
+    animation-duration: 0.01ms !important;
+    animation-iteration-count: 1 !important;
+    transition-duration: 0.01ms !important;
+    scroll-behavior: auto !important;
+  }
+}
+
+/* Disable backdrop-filter on mobile for performance */
+@media (max-width: 767px) {
+  .mobile-backdrop {
+    backdrop-filter: none !important;
+    -webkit-backdrop-filter: none !important;
+  }
+}