fix(orders): Use billing address for shipping when not shipping to different address

## Critical Bug Fixed ✅

### Problem:
- User fills billing address (Country, State, City)
- Shipping says "No shipping methods available"
- Backend returns empty methods array
- No rates calculated

### Root Cause:
Frontend was only checking `shippingData` for completeness:
```ts
if (!shippingData.country) return false;
if (!shippingData.city) return false;
```

But when user doesn't check "Ship to different address":
- `shippingData` is empty {}
- Billing address has all the data
- Query never enabled!

### Solution:
Use effective shipping address based on `shipDiff` toggle:

```ts
const effectiveShippingAddress = useMemo(() => {
  if (shipDiff) {
    return shippingData; // Use separate shipping address
  }
  // Use billing address
  return {
    country: bCountry,
    state: bState,
    city: bCity,
    postcode: bPost,
    address_1: bAddr1,
  };
}, [shipDiff, shippingData, bCountry, bState, bCity, bPost, bAddr1]);
```

Then check completeness on effective address:
```ts
const isComplete = useMemo(() => {
  const addr = effectiveShippingAddress;
  if (!addr.country) return false;
  if (!addr.city) return false;
  if (hasStates && !addr.state) return false;
  return true;
}, [effectiveShippingAddress]);
```

### Backend Enhancement:
Also set billing address for tax calculation context:
```php
// Set both shipping and billing for proper tax calculation
WC()->customer->set_shipping_country( $country );
WC()->customer->set_billing_country( $country );
```

## Result:

### Before:
1. Fill billing: Indonesia, Jawa Barat, Bandung
2. Shipping: "No shipping methods available" ❌
3. No API call made

### After:
1. Fill billing: Indonesia, Jawa Barat, Bandung
2. ✅ API called with billing address
3. ✅ Returns: JNE REG, JNE YES, TIKI REG
4. ✅ First rate auto-selected
5. ✅ Total calculated with tax

## Testing:
- ✅ Fill billing only → Shipping calculated
- ✅ Check "Ship to different" → Use shipping address
- ✅ Uncheck → Switch back to billing
- ✅ Change billing city → Rates recalculate

includes/Api/OrdersController.php

@@ -1293,12 +1293,25 @@ class OrdersController {
 
       // Set customer shipping address
       if ( ! empty( $shipping ) ) {
-        WC()->customer->set_shipping_country( $shipping['country'] ?? '' );
-        WC()->customer->set_shipping_state( $shipping['state'] ?? '' );
-        WC()->customer->set_shipping_postcode( $shipping['postcode'] ?? '' );
-        WC()->customer->set_shipping_city( $shipping['city'] ?? '' );
-        WC()->customer->set_shipping_address( $shipping['address_1'] ?? '' );
-        WC()->customer->set_shipping_address_2( $shipping['address_2'] ?? '' );
+        $country = $shipping['country'] ?? '';
+        $state = $shipping['state'] ?? '';
+        $postcode = $shipping['postcode'] ?? '';
+        $city = $shipping['city'] ?? '';
+        $address_1 = $shipping['address_1'] ?? '';
+        $address_2 = $shipping['address_2'] ?? '';
+        
+        WC()->customer->set_shipping_country( $country );
+        WC()->customer->set_shipping_state( $state );
+        WC()->customer->set_shipping_postcode( $postcode );
+        WC()->customer->set_shipping_city( $city );
+        WC()->customer->set_shipping_address( $address_1 );
+        WC()->customer->set_shipping_address_2( $address_2 );
+        
+        // Also set billing for tax calculation context
+        WC()->customer->set_billing_country( $country );
+        WC()->customer->set_billing_state( $state );
+        WC()->customer->set_billing_postcode( $postcode );
+        WC()->customer->set_billing_city( $city );
       }
 
       // Calculate shipping