Extends PATCH /admin/agents/:agentId with an optional userId to finally
wire Agent.userId (added in 010-identity-auth as schema-only, never
consumed by any workflow), with proactive role/duplicate-link checks
mirroring UsersService.create's own pre-check style.
Adds GET /agents/me/tickets and GET /admin/agents/:agentId/tickets,
sharing one TicketsService.listAssignedTo method, returning a dashboard-
ready summary (product, customer, priority, severity, status, SLA state)
of every ticket currently assigned to an agent — no such query existed
anywhere in the ticketing or orchestration modules before this. Backed by
a new Assignment @@index([agentId, isCurrent]).
Discovered while starting supporthub-web's 001-agent-admin-ui: its agent-
dashboard user story had no backend data source without this.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
