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_DataService/Fuchs_DataService.xml

@@ -37,5 +37,18 @@
             which <c>Program.cs</c> calls once at startup before any <see cref="T:fds.FdsMfr"/> use.
             </summary>
         </member>
+        <member name="T:fds.FdsDocumentNames">
+            <summary>
+            Download-filename sanitising shared by every path that hands a document to the browser —
+            stored documents (<see cref="M:fds.FdsMfr.GetReportDoc(System.Byte[]@,System.String,System.Boolean)"/>) and documents regenerated on a miss
+            (<c>IntranetController.HandleReportDoc</c>, ADR 0025) — so both produce the same name for the
+            same DocumentName. DocumentName is derived from the user-typed invoice title, so it can carry
+            path separators ("Wartung 2025/26"), stray editor markup and characters Windows rejects.
+            </summary>
+        </member>
+        <member name="M:fds.FdsDocumentNames.SafeFileName(System.String,System.String)">
+            <param name="documentName">Raw DocumentName (may be null, empty, or wrapped in &lt;p&gt;).</param>
+            <param name="fallback">Used when nothing usable remains after cleanup.</param>
+        </member>
     </members>
 </doc>