feat(126): invoice GUS field mapping fix (JDG/KRS heuristic)

MfWhitelistApiClient.lookupByNip() exposes is_jdg/krs from MF Biala Lista.
InvoiceController.nipLookup propagates is_jdg in JSON response.
invoice_form.php JS conditionally targets buyer_name (JDG) or
buyer_company_name (spolka z KRS); second field keeps zamowienie pre-fill.

Fixes apparent field swap on /orders/{id}/invoice/create after GUS lookup
for JDG (sole trader) where MF returns natural person in subject.name.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Core/Http/MfWhitelistApiClient.php

@@ -19,7 +19,7 @@ final class MfWhitelistApiClient
     }
 
     /**
-     * @return array{name: string, tax_no: string, regon: string, street: string, postal_code: string, city: string, country: string, status_vat: string, raw: array<string, mixed>}
+     * @return array{name: string, tax_no: string, regon: string, street: string, postal_code: string, city: string, country: string, status_vat: string, krs: string, is_jdg: bool, raw: array<string, mixed>}
      */
     public function lookupByNip(string $nip, ?string $date = null): array
     {
@@ -65,6 +65,8 @@ final class MfWhitelistApiClient
         $address = trim((string) ($subject['workingAddress'] ?? $subject['residenceAddress'] ?? ''));
         ['street' => $street, 'postal_code' => $postalCode, 'city' => $city] = $this->parseAddress($address);
 
+        $krs = trim((string) ($subject['krs'] ?? ''));
+
         return [
             'name' => $name,
             'tax_no' => trim((string) ($subject['nip'] ?? $cleanNip)),
@@ -74,6 +76,8 @@ final class MfWhitelistApiClient
             'city' => $city,
             'country' => 'PL',
             'status_vat' => trim((string) ($subject['statusVat'] ?? '')),
+            'krs' => $krs,
+            'is_jdg' => $krs === '',
             'raw' => $subject,
         ];
     }

src/Modules/Accounting/InvoiceController.php

@@ -55,6 +55,7 @@ final class InvoiceController
                 'country' => $data['country'],
                 'regon' => $data['regon'],
                 'status_vat' => $data['status_vat'],
+                'is_jdg' => (bool) ($data['is_jdg'] ?? false),
             ],
         ]);
     }