feat(suppliers)!: full customers model - structured address + custom fields

The dodavatele modal is now an exact mirror of the customers modal
(minus the PDF field-order picker): Nazev+ARES, Ulice, Mesto+PSC, Zeme,
ICO+ARES, DIC, and the same "Vlastni pole" editor (maxWidth md).

Two migrations on sklad_suppliers:
- structured street/city/postal_code/country replace the free-text
  address blob (best-effort split: street / PSC regex / city)
- custom_fields LONGTEXT replaces contact_person/email/phone/notes;
  existing values are preserved as labeled custom fields

The encode/decode of the custom_fields blob is shared with customers
via the new utils/custom-fields.ts. The PO PDF supplier block renders
the structured address + custom-field lines like the customer block;
the supplier picker/detail selects and types follow. Legacy clients
sending the dropped keys are silently stripped (tested). Suppliers
list shows Ulice/Mesto instead of the dropped contact columns; search
covers name/ico/city.

BREAKING CHANGE: sklad_suppliers.address, contact_person, email,
phone, notes columns dropped (data migrated); deploy must run
prisma migrate deploy + generate.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/pages/IssuedOrderDetail.tsx

@@ -207,9 +207,10 @@ export default function IssuedOrderDetail() {
           name: form.supplier_name || `Dodavatel #${form.supplier_id}`,
           ico: null,
           dic: null,
-          address: null,
-          email: null,
-          phone: null,
+          street: null,
+          city: null,
+          postal_code: null,
+          country: null,
         },
       ];
     }