feat: Mobile chart optimization + VIP customer settings

## Task 4: Mobile Chart Optimization ✅

**Problem:** Too many data points = tight/crowded lines on mobile

**Solution:** Horizontal scroll container

**Implementation:**
- ChartCard component enhanced with mobile scroll
- Calculates minimum width based on data points (40px per point)
- Desktop: Full width responsive
- Mobile: Fixed width chart in scrollable container

```tsx
// ChartCard.tsx
const mobileMinWidth = Math.max(600, dataPoints * 40);

<div className="overflow-x-auto -mx-6 px-6 md:mx-0 md:px-0">
  <div style={{ minWidth: `${mobileMinWidth}px` }}>
    {children}
  </div>
</div>
```

**Benefits:**
- ✅ All data visible (no loss)
- ✅ Natural swipe gesture
- ✅ Readable spacing
- ✅ Works for all chart types
- ✅ No data aggregation needed

---

## Task 5: VIP Customer Settings ✅

**New Feature:** Configure VIP customer qualification criteria

### Backend (PHP)

**Files Created:**
- `includes/Compat/CustomerSettingsProvider.php`
  - VIP settings management
  - VIP detection logic
  - Customer stats calculation

**API Endpoints:**
- `GET /store/customer-settings` - Fetch settings
- `POST /store/customer-settings` - Save settings

**Settings:**
```php
woonoow_vip_min_spent = 1000
woonoow_vip_min_orders = 10
woonoow_vip_timeframe = 'all' | '30' | '90' | '365'
woonoow_vip_require_both = true
woonoow_vip_exclude_refunded = true
```

**VIP Detection:**
```php
CustomerSettingsProvider::is_vip_customer($customer_id)
CustomerSettingsProvider::get_vip_stats($customer_id)
```

### Frontend (React)

**Files Created:**
- `admin-spa/src/routes/Settings/Customers.tsx`

**Features:**
- 💰 Minimum total spent (currency input)
- �� Minimum order count (number input)
- 📅 Timeframe selector (all-time, 30/90/365 days)
- ⚙️ Require both criteria toggle
- 🚫 Exclude refunded orders toggle
- 👑 Live preview of VIP qualification

**Navigation:**
- Added to Settings menu
- Route: `/settings/customers`
- Position: After Tax, before Notifications

---

## Summary

✅ **Mobile Charts:** Horizontal scroll for readable spacing
✅ **VIP Settings:** Complete backend + frontend implementation

**Mobile Chart Strategy:**
- Minimum 600px width
- 40px per data point
- Smooth horizontal scroll
- Desktop remains responsive

**VIP Customer System:**
- Flexible qualification criteria
- Multiple timeframes
- AND/OR logic support
- Refunded order exclusion
- Ready for customer list integration

**All tasks complete!** 🎉

admin-spa/src/nav/tree.ts

@@ -109,6 +109,7 @@ function getStaticFallbackTree(): MainNode[] {
         { label: 'Payments', mode: 'spa' as const, path: '/settings/payments' },
         { label: 'Shipping & Delivery', mode: 'spa' as const, path: '/settings/shipping' },
         { label: 'Tax', mode: 'spa' as const, path: '/settings/tax' },
+        { label: 'Customers', mode: 'spa' as const, path: '/settings/customers' },
         { label: 'Notifications', mode: 'spa' as const, path: '/settings/notifications' },
         { label: 'Developer', mode: 'spa' as const, path: '/settings/developer' },
       ],