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

admin-spa/src/routes/Orders/partials/OrderForm.tsx

@@ -185,26 +185,43 @@ export default function OrderForm({
     enabled: items.length > 0,
   });
 
+  // Get effective shipping address (use billing if not shipping to different address)
+  const effectiveShippingAddress = React.useMemo(() => {
+    if (shipDiff) {
+      return shippingData;
+    }
+    // Use billing address
+    return {
+      country: bCountry,
+      state: bState,
+      city: bCity,
+      postcode: bPost,
+      address_1: bAddr1,
+      address_2: '',
+    };
+  }, [shipDiff, shippingData, bCountry, bState, bCity, bPost, bAddr1]);
+
   // Check if shipping address is complete enough to calculate rates
   const isShippingAddressComplete = React.useMemo(() => {
+    const addr = effectiveShippingAddress;
     // Need at minimum: country, state (if applicable), city
-    if (!shippingData.country) return false;
-    if (!shippingData.city) return false;
+    if (!addr.country) return false;
+    if (!addr.city) return false;
     // If country has states, require state
-    const countryStates = states[shippingData.country];
-    if (countryStates && Object.keys(countryStates).length > 0 && !shippingData.state) {
+    const countryStates = states[addr.country];
+    if (countryStates && Object.keys(countryStates).length > 0 && !addr.state) {
       return false;
     }
     return true;
-  }, [shippingData.country, shippingData.state, shippingData.city, states]);
+  }, [effectiveShippingAddress, states]);
 
   // Calculate shipping rates dynamically
   const { data: shippingRates, isLoading: shippingLoading } = useQuery({
-    queryKey: ['shipping-rates', items.map(i => ({ product_id: i.product_id, qty: i.qty })), shippingData.country, shippingData.state, shippingData.city, shippingData.postcode, shippingData.address_1],
+    queryKey: ['shipping-rates', items.map(i => ({ product_id: i.product_id, qty: i.qty })), effectiveShippingAddress.country, effectiveShippingAddress.state, effectiveShippingAddress.city, effectiveShippingAddress.postcode, effectiveShippingAddress.address_1],
     queryFn: async () => {
       return api.post('/shipping/calculate', {
         items: items.map(i => ({ product_id: i.product_id, qty: i.qty })),
-        shipping: shippingData,
+        shipping: effectiveShippingAddress,
       });
     },
     enabled: isShippingAddressComplete && items.length > 0,