feat(helpdesk): add team workload dashboard with per-agent metrics

New standalone page (helpdesk/team) showing support agent workload
aggregated from BC tickets. KPI bar (open, unassigned, avg age, resolved),
per-agent table sorted by open tickets, period selector (30/90/180/365d).
Global OData query via getTicketsForTeam() without customer filter.
New permission helpdesk.team-workload.view with admin role assignment.
Includes 6 PHPUnit tests for buildTeamWorkloadDashboard().

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

modules/helpdesk/lib/Module/Helpdesk/Service/DebitorCacheControl.php

@@ -82,6 +82,11 @@ final class DebitorCacheControl
         return 'module.helpdesk.debitor.v1.escalation-definitions.' . $tenantScope;
     }
 
+    public static function teamWorkloadKey(string $tenantScope): string
+    {
+        return 'module.helpdesk.team.v1.workload.' . $tenantScope;
+    }
+
     /**
      * @return array<int, string>
      */