feat: Implement mobile-first navigation with bottom bar and FAB

Implemented mobile-optimized navigation structure:

1. Bottom Navigation (Mobile Only)
   - 5 items: Dashboard, Orders, Products, Customers, More
   - Fixed at bottom, always visible
   - Thumb-friendly positioning
   - Active state indication
   - Hidden on desktop (md:hidden)

2. More Menu Page
   - Overflow menu for Coupons and Settings
   - Clean list layout with icons
   - Descriptions for each item
   - Chevron indicators

3. FAB (Floating Action Button)
   - Context-aware system via FABContext
   - Fixed bottom-right (72px from bottom)
   - Hidden on desktop (md:hidden)
   - Ready for contextual actions per page

4. FAB Context System
   - Global state for FAB configuration
   - setFAB() / clearFAB() methods
   - Supports icon, label, onClick, visibility
   - Allows pages to control FAB behavior

5. Layout Updates
   - Added pb-14 to main for bottom nav spacing
   - BottomNav and FAB in mobile fullscreen layout
   - Wrapped app with FABProvider

Structure (Mobile):
┌─────────────────────────────────┐
│ App Bar (will hide on scroll)   │
├─────────────────────────────────┤
│ Page Header (sticky, contextual)│
├─────────────────────────────────┤
│ Submenu (sticky)                │
├─────────────────────────────────┤
│ Content (scrollable)            │
│                        [+] FAB  │
├─────────────────────────────────┤
│ Bottom Nav (fixed)              │
└─────────────────────────────────┘

Next Steps:
- Implement scroll-hide for app bar
- Add contextual FAB per page
- Test on real devices

Files Created:
- BottomNav.tsx: Bottom navigation component
- More/index.tsx: More menu page
- FABContext.tsx: FAB state management
- FAB.tsx: Floating action button component
- useScrollDirection.ts: Scroll detection hook

Files Modified:
- App.tsx: Added bottom nav, FAB, More route, providers

admin-spa/src/hooks/useScrollDirection.ts

@@ -0,0 +1,30 @@
+import { useState, useEffect } from 'react';
+
+export function useScrollDirection() {
+  const [scrollDirection, setScrollDirection] = useState<'up' | 'down'>('up');
+  const [lastScrollY, setLastScrollY] = useState(0);
+
+  useEffect(() => {
+    const handleScroll = () => {
+      const currentScrollY = window.scrollY;
+      
+      if (currentScrollY > lastScrollY && currentScrollY > 50) {
+        // Scrolling down
+        setScrollDirection('down');
+      } else if (currentScrollY < lastScrollY) {
+        // Scrolling up
+        setScrollDirection('up');
+      }
+      
+      setLastScrollY(currentScrollY);
+    };
+
+    window.addEventListener('scroll', handleScroll, { passive: true });
+    
+    return () => {
+      window.removeEventListener('scroll', handleScroll);
+    };
+  }, [lastScrollY]);
+
+  return scrollDirection;
+}