feat: Enhance error logging for PDF preview failures and SQL timeouts

- Implemented a new method `ShapeTableNames` to gather entity and navigation table names, ensuring no blanks or duplicates are included.
- Updated `FdsMfrClient` to handle cases where schema queries return no tables, logging appropriate warnings and preventing misleading errors.
- Introduced `PdfPreviewAsync` in `IntranetController` to manage PDF preview rendering, capturing detailed logs for failures and notifying users with readable error messages.
- Added comprehensive unit tests for error logging and table name shaping to ensure robustness and correctness.
- Documented decision to persist user action failures to the `fds__admin_logdebug` table, enhancing support diagnostics.

Fuchs/Observability/FuchsTelemetry.cs

@@ -57,6 +57,9 @@ public static class FuchsTelemetry
     public static readonly Counter<long> InvoiceInlineImageFetches =
         Meter.CreateCounter<long>("fuchs.invoice.inlineimages.fetches", "{fetch}",
             "Invoice-text image fetches for inline PDF rendering (ADR 0018), tagged by outcome.");
+    public static readonly Counter<long> PdfPreviews =
+        Meter.CreateCounter<long>("fuchs.pdf.previews", "{preview}",
+            "PDF preview requests (draft/invoice/reminder/report image previews), tagged by endpoint and outcome.");
 
     // ── Performance histograms (durations in milliseconds) ───────────────────
     public static readonly Histogram<double> PdfRenderDuration =