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_en.json

@@ -284,5 +284,15 @@
   "Advanced options": "Advanced options",
   "Min. overdue": "Min. overdue",
   "Min. age": "Min. age",
-  "Min. open": "Min. open"
+  "Min. open": "Min. open",
+  "Team": "Team",
+  "Team workload": "Team workload",
+  "Support agent": "Support agent",
+  "Open": "Open",
+  "Critical (>48h open)": "Critical (>48h open)",
+  "Avg. age (h)": "Avg. age (h)",
+  "Resolved in period": "Resolved in period",
+  "Not assigned": "Not assigned",
+  "Could not load team dashboard.": "Could not load team dashboard.",
+  "No team data available.": "No team data available."
 }