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>

prisma/schema.prisma

@@ -804,18 +804,18 @@ model sklad_categories {
 }
 
 model sklad_suppliers {
-  id             Int       @id @default(autoincrement())
-  name           String    @db.VarChar(255)
-  ico            String?   @db.VarChar(20)
-  dic            String?   @db.VarChar(20)
-  contact_person String?   @db.VarChar(255)
-  email          String?   @db.VarChar(255)
-  phone          String?   @db.VarChar(50)
-  address        String?   @db.Text
-  notes          String?   @db.Text
-  is_active      Boolean   @default(true)
-  created_at     DateTime? @default(now()) @db.DateTime(0)
-  modified_at    DateTime? @db.DateTime(0)
+  id            Int       @id @default(autoincrement())
+  name          String    @db.VarChar(255)
+  ico           String?   @db.VarChar(20)
+  dic           String?   @db.VarChar(20)
+  street        String?   @db.VarChar(255)
+  city          String?   @db.VarChar(255)
+  postal_code   String?   @db.VarChar(20)
+  country       String?   @db.VarChar(100)
+  custom_fields String?   @db.LongText
+  is_active     Boolean   @default(true)
+  created_at    DateTime? @default(now()) @db.DateTime(0)
+  modified_at   DateTime? @db.DateTime(0)
 
   receipts      sklad_receipts[]
   issued_orders issued_orders[]