Add German localization and styling for administration module

- Introduced new JavaScript file `fis.admin_txt_de.js` for German translations of administration-related terms and messages.
- Created `fis.admin.css` for styling the administration interface, including layout, cards, and buttons.
- Added `fis.admin.de.js` for the main functionality of the administration module, implementing features such as system status checks and email testing.
- Minified version of the German JavaScript file created as `fis.admin.de.min.js`.
- Minified CSS file created as `fis.admin.min.css` for optimized loading.

Fuchs/Observability/FuchsTelemetry.cs

@@ -51,6 +51,9 @@ public static class FuchsTelemetry
         Meter.CreateCounter<long>("fuchs.blobstorage.uploads", "{upload}", "Number of documents successfully archived to Azure Blob Storage.");
     public static readonly Counter<long> BlobUploadsFailed =
         Meter.CreateCounter<long>("fuchs.blobstorage.uploads.failed", "{upload}", "Number of documents that failed to archive to Azure Blob Storage.");
+    public static readonly Counter<long> SystemProbes =
+        Meter.CreateCounter<long>("fuchs.systemstatus.probes", "{probe}",
+            "Admin system-status connectivity probes executed, tagged by component and outcome.");
 
     // ── Performance histograms (durations in milliseconds) ───────────────────
     public static readonly Histogram<double> PdfRenderDuration =