feat(workflow): add WorkflowListener with per-event helpers

[mpge]

Summary

Final piece of the workflow stack for Phoenix. Provides a thin wrapper (WorkflowListener) that bridges domain events into WorkflowRunner.run_for_event/2.

Each helper maps an event to a canonical workflow trigger name (matching the 12-event set in WorkflowEngine.trigger_events/0) and fires the runner in a supervised Task so a slow workflow never blocks the mutation that fired it.

Opt-in wire-up

Phoenix doesn't auto-emit ApplicationEvents the way Spring or EventEmitter2 do, so host apps opt in by calling these helpers from their TicketService wrappers or post-write PubSub / Oban handlers:

# After creating a ticket
WorkflowListener.ticket_created(ticket)

# After a reply
WorkflowListener.reply_created(reply)

Per-event helpers

ticket_created/1, ticket_updated/1, ticket_status_changed/1, ticket_priority_changed/1, ticket_assigned/1, ticket_reopened/1, ticket_tagged/1, ticket_department_changed/1, reply_created/1, sla_breached/1, sla_warning/1.

Failure semantics

Runner failures are caught inside the spawned task and emitted via Logger.error/1. They never propagate back to the caller — matches the "one bad workflow never blocks the mutation" rule applied everywhere else in this stack.

Complete chain

TicketService mutation
  → WorkflowListener.<event>(ticket)
  → Task / Task.Supervisor
  → WorkflowRunner.run_for_event
  → WorkflowEngine (conditions) + WorkflowExecutor (actions)
  → workflow_logs row

Dependencies

• Stacked on feat(workflow): add WorkflowRunner for event-driven workflow firing #31 (feat/workflow-runner), which is stacked on feat(workflow): add WorkflowExecutor for action dispatch #30 (feat/workflow-executor).
• Merge order: feat(workflow): add WorkflowExecutor for action dispatch #30 → feat(workflow): add WorkflowRunner for event-driven workflow firing #31 → this PR.

Test plan

• 15 ExUnit tests covering fire/2 argument validation, reply_created/1 shape handling, and interface checks for every per-event helper
• Integration with real Ecto repo covered once a test repo is configured in a follow-up