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/i18n/default_de.json

@@ -284,5 +284,15 @@
   "Advanced options": "Erweiterte Optionen",
   "Min. overdue": "Mind. überfällig",
   "Min. age": "Mindestalter",
-  "Min. open": "Mind. offen"
+  "Min. open": "Mind. offen",
+  "Team": "Team",
+  "Team workload": "Team-Auslastung",
+  "Support agent": "Support-Mitarbeiter",
+  "Open": "Offen",
+  "Critical (>48h open)": "Kritisch (>48h offen)",
+  "Avg. age (h)": "Ø Alter (h)",
+  "Resolved in period": "Gelöst im Zeitraum",
+  "Not assigned": "Nicht zugewiesen",
+  "Could not load team dashboard.": "Team-Dashboard konnte nicht geladen werden.",
+  "No team data available.": "Keine Team-Daten verfügbar."
 }