iOS: Kaufpreis + Belege am Einzelstück

ItemEditView bekommt einen Kaufpreis (Betrag + CHF/EUR) und eine Beleg-Sektion:
Rechnung/Garantieschein als Bild (Fotoauswahl) oder PDF (Datei-Import)
hochladen, ansehen (QuickLook) und loeschen. Nach einem PDF-Upload schlaegt der
Server "Garantie bis" und Kaufpreis vor – per Knopf uebernehmbar. Item-Model um
priceCents/currency/documents erweitert; Client-Methoden fuer Upload, Download
und Loeschen der Belege.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ios/Sources/APIClient.swift

@@ -182,6 +182,36 @@ actor APIClient {
         try await sendNoContent(request)
     }
 
+    func uploadItemDocument(itemId: Int, data: Data, filename: String,
+                            contentType: String) async throws -> ItemDocumentUpload {
+        var request = try makeRequest("/items/\(itemId)/documents", method: "POST")
+        let boundary = "Boundary-\(UUID().uuidString)"
+        request.setValue("multipart/form-data; boundary=\(boundary)",
+                         forHTTPHeaderField: "Content-Type")
+        let safeName = filename.replacingOccurrences(of: "\"", with: "")
+        var body = Data()
+        body.append("--\(boundary)\r\n".data(using: .utf8)!)
+        body.append("Content-Disposition: form-data; name=\"file\"; filename=\"\(safeName)\"\r\n"
+            .data(using: .utf8)!)
+        body.append("Content-Type: \(contentType)\r\n\r\n".data(using: .utf8)!)
+        body.append(data)
+        body.append("\r\n--\(boundary)--\r\n".data(using: .utf8)!)
+        request.httpBody = body
+        return try await send(request, as: ItemDocumentUpload.self)
+    }
+
+    func itemDocumentData(itemId: Int, docId: Int) async throws -> Data {
+        let request = try makeRequest("/items/\(itemId)/documents/\(docId)")
+        let (data, response) = try await URLSession.shared.data(for: request)
+        try check(response, data: data)
+        return data
+    }
+
+    func deleteItemDocument(itemId: Int, docId: Int) async throws {
+        try await sendNoContent(
+            try makeRequest("/items/\(itemId)/documents/\(docId)", method: "DELETE"))
+    }
+
     func deleteItem(id: Int) async throws {
         try await sendNoContent(try makeRequest("/items/\(id)", method: "DELETE"))
     }