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>

db/init/init.sql

@@ -1551,7 +1551,7 @@ JOIN permissions p ON p.`key` IN (
   'mail_log.view', 'api_audit.view', 'system_audit.view', 'system_audit.purge',
   'stats.view', 'system_info.view',
   'roles.assign_all',
-  'helpdesk.access', 'helpdesk.settings.manage'
+  'helpdesk.access', 'helpdesk.settings.manage', 'helpdesk.team-workload.view'
 )
 WHERE r.description IN ('Admin', 'Administrator') OR r.id = 1
 ON DUPLICATE KEY UPDATE role_id = role_id;