feat: move test buttons to right panel, add user auth dialog for reports

Move Start/Stop/Report buttons from the middle panel to the top of
TestPanelView (automated tests section), matching the old application
layout. Remove inline Operator/Client text fields — operator identity
now comes from a UserCheckDialog (username/password) shown before the
existing ReportDialog. Add credential storage to ConfigurationService.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Models/BenchConfiguration.cs

@@ -135,6 +135,12 @@ namespace HC_APTBS.Models
         /// <summary>Absolute path to the company logo image for the report.</summary>
         public string ReportLogoPath { get; set; } = string.Empty;
 
+        /// <summary>
+        /// Comma-separated <c>user:password</c> credential pairs for operator authentication
+        /// before report generation.
+        /// </summary>
+        public string Users { get; set; } = "admin:admin";
+
         // ── K-Line port ───────────────────────────────────────────────────────
 
         /// <summary>Serial port or FTDI device identifier for the K-Line interface.</summary>