Restore legacy parity gaps lost in the VB.NET → C# migration

Close functional regressions found by comparing the legacy applications
(Intranet_Legacy/) against their C# counterparts:

- ProcessWebComService: send attachments inline (base64) with the
  push_com POST so invoice/reminder PDFs are attached again.
- FuchsPdf: wire GetPaycode into ApplyInvoice/ApplyReminder to restore
  the SEPA giro-code payment QR, and restore the full standard invoice
  text block (§35a labor-cost note, Akonto text, §14/§48 notes, AGB,
  Steuernummer, Verrechnungssätze, etc.).
- IntranetController: restore changepassword validation (password
  strength, confirmation match, current-password verification) and the
  mfr empty-id OData $metadata response.
- Reports: port the ocms_visualization engine to C# (FuchsVisualization)
  and wire FuchsReports.ProcessFdsRequest to render generic/
  generic_content/chart reports instead of returning an empty OK stub.

Adds smoke tests for the giro QR generator and report page builder.

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

Fuchs/Services/ProcessWebComService.cs

@@ -66,14 +66,30 @@ public class ProcessWebComService : IComService
 
         try
         {
+            // Attachments are transmitted inline as base64 in the same push_com POST.
+            // Each entry: { filename, mimeType, contentBase64 }.
+            var attachmentPayload = (attachments ?? new Dictionary<string, byte[]>())
+                .Where(kv => kv.Value is { Length: > 0 })
+                .Select(kv => new
+                {
+                    filename      = kv.Key,
+                    mimeType      = GuessMimeType(kv.Key),
+                    contentBase64 = Convert.ToBase64String(kv.Value)
+                })
+                .ToArray();
+
             var payload = new
             {
-                comType   = "email",
-                recipient = email,
+                comType     = "email",
+                recipient   = email,
                 subject,
-                body
+                body,
+                attachments = attachmentPayload
             };
 
+            _logger.LogDebug("SendEmailAsync ref={Reference} to={Email} attachments={Count}",
+                reference, email, attachmentPayload.Length);
+
             var (ok, responseBody) = await PostToApiAsync("push_com", payload);
             if (ok)
             {
@@ -190,6 +206,24 @@ public class ProcessWebComService : IComService
         return "";
     }
 
+    private static string GuessMimeType(string filename) =>
+        Path.GetExtension(filename).ToLowerInvariant() switch
+        {
+            ".pdf"  => "application/pdf",
+            ".png"  => "image/png",
+            ".jpg" or ".jpeg" => "image/jpeg",
+            ".gif"  => "image/gif",
+            ".txt"  => "text/plain",
+            ".csv"  => "text/csv",
+            ".xml"  => "application/xml",
+            ".zip"  => "application/zip",
+            ".doc"  => "application/msword",
+            ".docx" => "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+            ".xls"  => "application/vnd.ms-excel",
+            ".xlsx" => "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+            _       => "application/octet-stream"
+        };
+
     private static bool IsValidEmail(string email)
     {
         try