fix: fund report layout refactor and chart renderer fix

- FundAnagraficaRenderer: unified header style (DrawColHeader), DrawPerfGrid returns float, chart embedded in anagrafica section
- FundReportController: simplify filename to {isin}.pdf
- SkiaChartRendererV2: minor fix affecting certificate chart

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

CertReports.Syncfusion/Controllers/FundReportController.cs

@@ -93,7 +93,7 @@ public class FundReportController : ControllerBase
             var pdfBytes    = await _orchestrator.GenerateReportAsync(isin, branding);
             var disposition = inline ? "inline" : "attachment";
             Response.Headers.Append("Content-Disposition",
-                $"{disposition}; filename=fund_{isin}.pdf");
+                $"{disposition}; filename={isin}.pdf");
             return File(pdfBytes, "application/pdf");
         }
         catch (InvalidOperationException ex) when (ex.Message.Contains("Nessun dato"))