Add Cc (Zusatzempfänger) recipient support for invoice emails

Lets an invoice carry an additional Cc recipient alongside the primary
SendToEmail, sent via the ProcessWeb mailer API. Honors the
Fuchs:Email:OverrideRecipient dev safety net: when the override is
active, Cc is dropped entirely (only the single override inbox is
ever reached), never leaked to it.

- IComService.SendEmailAsync / ProcessWebComService: new optional
  `cc` parameter, included in the mailer payload only when non-empty.
- FdsInvoiceData.RawInvoiceEmailCc + BuildInvoiceParams: reads
  `new.invoiceemailcc`, posts @SendToEmailCc.
- IntranetController.Requests: reads SendToEmailCc from the loaded
  invoice row and passes it through on send/resend.
- Fuchs_Database: SendToEmailCc column on fds__invoices, threaded
  through fds__createInvoice/fds__setInvoice/fds__getInvoice and the
  fds__tt__invoice_base/_core table types.
- fis.req_txt_de.js: "Zusatzempfänger (CC)" field label.
- Tests: ProcessWebComServiceTests (Cc included/omitted/dropped under
  override); SystemStatusServiceTests mocks updated for the new
  IComService.SendEmailAsync parameter.

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

Fuchs/code/FdsInvoiceData.cs

@@ -133,6 +133,8 @@ public class FdsInvoiceData
     // -- Raw form properties (used by parameter mapping) -----------------------
     internal string RawInvoiceAddress  => NewValues?.nz("invoiceaddress") ?? "";
     internal string RawInvoiceEmail    => NewValues?.nz("invoiceemail").Trim() ?? "";
+    /// <summary>Additional recipient ("Zusatzempfänger") sent as Cc alongside the primary invoice email.</summary>
+    internal string RawInvoiceEmailCc  => NewValues?.nz("invoiceemailcc").Trim() ?? "";
     internal string RawCustomValues    => NewValues?.nz("CustomValues").Trim() ?? "";
     internal string RawProvisionPeriod => NewValues?.nz("provisionperiod") ?? "";
     internal string[] RawProvisionLocation =>
@@ -179,6 +181,7 @@ public class FdsInvoiceData
             SQL_BigInt("@CustomerId",           Admin?.nz("customerid") ?? ""),
             SQL_VarChar("@SendToAddress",       RawInvoiceAddress),
             SQL_NVarChar("@SendToEmail",        RawInvoiceEmail),
+            SQL_NVarChar("@SendToEmailCc",      RawInvoiceEmailCc, dbNull_IfEmpty: true),
             SQL_NVarChar("@ProvisionPeriod",    RawProvisionPeriod, dbNull_IfEmpty: true),
             SQL_NVarChar("@CustomValues",       RawCustomValues, dbNull_IfEmpty: true),
             SQL_NVarChar("@SendToAddressJson",  SendToAddressJsonForPersist(), dbNull_IfEmpty: true),