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.Tests/FuchsReportRenderTests.cs

@@ -0,0 +1,52 @@
+using Fuchs.intranet;
+using Xunit;
+
+namespace Fuchs.Tests;
+
+/// <summary>
+/// Smoke tests for the non-DB parts of the restored report engine and the
+/// giro-code QR generator. The SQL-driven report rendering itself requires a
+/// live report catalog and is validated separately against the database.
+/// </summary>
+public class FuchsReportRenderTests
+{
+    [Fact]
+    public void GetPaycode_ProducesNonEmptyBitmap()
+    {
+        using var bmp = FuchsPdf.GetPaycode(
+            iban: "DE52301502000002091478", bic: "WELADED1KSD",
+            name: "Sebastian Fuchs Bad und Heizung", amount: 123.45m, purpose: "Rechnung 4711");
+        Assert.NotNull(bmp);
+        Assert.True(bmp.Width  > 0);
+        Assert.True(bmp.Height > 0);
+    }
+
+    [Fact]
+    public void HtmlPage_Web_FallbackShell_EmbedsContentTitleAndReload()
+    {
+        var page = new FuchsHtmlPage("My Report", templatePath: "", queryDuration: 0)
+        {
+            ReloadSeconds = 60
+        };
+        page.Add("<div id=\"frm\">hello</div>");
+
+        string html = page.ToHtml(FdsDestination.web);
+
+        Assert.Contains("hello", html);
+        Assert.Contains("My Report", html);                 // title injected
+        Assert.Contains("http-equiv=\"refresh\"", html);    // reload meta injected
+        Assert.Contains("content=\"60\"", html);
+    }
+
+    [Fact]
+    public void HtmlPage_Content_OmitsReloadAndTitleChrome()
+    {
+        var page = new FuchsHtmlPage("Ignored", templatePath: "");
+        page.Add("<span>fragment</span>");
+
+        string html = page.ToHtml(FdsDestination.content);
+
+        Assert.Contains("fragment", html);
+        Assert.DoesNotContain("http-equiv=\"refresh\"", html);
+    }
+}