Refactor document name sanitization for consistent filename generation

- Introduced FdsDocumentNames class to centralize the logic for sanitizing document names used in downloads.
- Updated FdsMfr to utilize the new SafeFileName method for generating safe filenames.
- Enhanced documentation for FdsDocumentNames and its methods to clarify usage and purpose.
- Added global.json file to configure testing framework settings.

Fuchs.Tests/ReportDocFileNameTests.cs

@@ -26,8 +26,59 @@ public class ReportDocFileNameTests
     [InlineData("")]
     [InlineData("   ")]
     [InlineData("<p></p>")]
+    [InlineData("<p> </p>")]
     public void SafeDocumentFileName_EmptyDocumentName_UsesFallback(string? documentName)
     {
         Assert.Equal("Rechnung_W7VAL.pdf", IntranetController.SafeDocumentFileName(documentName!, "Rechnung_W7VAL.pdf"));
     }
+
+    /// <summary>
+    /// The stored-document path (<c>FdsMfr.GetReportDoc</c>) replaced exactly these characters
+    /// before the sanitiser was shared: <c>= &gt; | ! &lt; /</c>. The shared helper must still
+    /// produce the identical result for them — unifying the two paths may not loosen either.
+    /// </summary>
+    [Theory]
+    [InlineData("a>b|c!d<e/f=g.pdf", "a_b_c_d_e_f_g.pdf")]
+    [InlineData("<p>Summe=100!.pdf</p>", "Summe_100_.pdf")]
+    public void SafeFileName_KeepsEveryReplacementTheStoredDocumentPathMade(string documentName, string expected)
+    {
+        Assert.Equal(expected, fds.FdsDocumentNames.SafeFileName(documentName, "X.pdf"));
+    }
+
+    /// <summary>
+    /// Characters the old stored-document path did NOT catch but Windows rejects — the reason
+    /// the sanitiser was unified (code review on ADR 0025): a stored and a regenerated document
+    /// must never diverge in filename safety.
+    /// </summary>
+    [Theory]
+    [InlineData("Angebot A\\B.pdf", "Angebot A_B.pdf")]
+    [InlineData("Re: 2026.pdf", "Re_ 2026.pdf")]
+    [InlineData("x*y?z\".pdf", "x_y_z_.pdf")]
+    [InlineData("tab\there.pdf", "tab_here.pdf")]
+    public void SafeFileName_ReplacesInvalidCharsTheStoredDocumentPathMissed(string documentName, string expected)
+    {
+        Assert.Equal(expected, fds.FdsDocumentNames.SafeFileName(documentName, "X.pdf"));
+    }
+
+    [Theory]
+    [InlineData("Rechnung R2026-0258.pdf")]
+    [InlineData("Wartung 2025/26 R2026-0001.pdf")]
+    [InlineData("a>b|c!d<e/f=g.pdf")]
+    [InlineData("Angebot A\\B: \"x\" <y>|z?*.pdf")]
+    [InlineData("<p></p>")]
+    [InlineData(null)]
+    public void SafeDocumentFileName_MatchesSharedSanitiserForEveryInput(string? documentName)
+    {
+        Assert.Equal(
+            fds.FdsDocumentNames.SafeFileName(documentName, "Rechnung_X.pdf"),
+            IntranetController.SafeDocumentFileName(documentName!, "Rechnung_X.pdf"));
+    }
+
+    [Fact]
+    public void SafeFileName_ReturnsFallbackVerbatim_WhenNothingUsableRemains()
+    {
+        // The fallback is the caller's responsibility and is not sanitised or second-guessed.
+        Assert.Equal("W7VAL", fds.FdsDocumentNames.SafeFileName("<p></p>", "W7VAL"));
+        Assert.Equal("", fds.FdsDocumentNames.SafeFileName("", ""));
+    }
 }