Fix kiosk SignalR group: set ViewBag.CompanyId so tablet joins correct hub group

Without this, data-company-id was empty and the JS connected to kiosk- (no ID),
so StartSession signals never reached the tablet.

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

src/PowderCoating.Web/Controllers/KioskController.cs

@@ -669,6 +669,7 @@ public class KioskController : Controller
     /// <summary>Sets ViewBag properties needed by _KioskLayout from a Company entity.</summary>
     private async Task PopulateKioskViewBag(Company company)
     {
+        ViewBag.CompanyId      = company.Id;
         ViewBag.CompanyName    = company.CompanyName;
         ViewBag.CompanyLogoUrl = !string.IsNullOrEmpty(company.LogoFilePath)
             ? Url.Action("Logo", "Kiosk")