feat(workflow): delay action with deferred job queue

[mpge]

Summary

Adds the `delay` workflow action as a ninth entry in the catalog. Splits execution around a wait clause: actions before the delay run inline, remaining actions are persisted as a `DeferredWorkflowJob` row with `runAt = now + N seconds`. A `@Scheduled` poller on `WorkflowExecutorService` (60s cadence, matching SnoozeScheduler) picks up due pending jobs, rehydrates the ticket, resumes the saved action sequence, and flips status to `done` / `failed`. Rows are audit-retained.

What's added

• `DeferredWorkflowJob` entity — `(ticket_id, remaining_actions JSON, run_at, status, last_error)` with a composite `(status, run_at)` index for efficient polling
• `DeferredWorkflowJobRepository` — single derived query `findByStatusAndRunAtLessThanEqual`
• New branch in `WorkflowExecutorService.execute` — when `type: "delay"` is seen, serialize the `actions[i+1:]` suffix + save + return
• `@Scheduled` `runDueDeferredJobs()` polling method on the same executor (mirrors how the NestJS reference keeps the poller co-located with the executor rather than factoring out a separate scheduler component)
• 4 new unit tests: pre-delay action runs + post-delay doesn't + DeferredWorkflowJob persisted correctly; invalid seconds skips cleanly; poller resumes + marks done; poller handles missing ticket with `failed` status

Why

Ports escalated-nestjs#26 to the Spring plugin. The other eight workflow actions already in `feat/workflow-executor` (`change_priority`, `change_status`, `assign_agent`, `set_department`, `add_tag`, `remove_tag`, `add_note`, `insert_canned_reply`) now have parity with the NestJS reference; `delay` was the last missing entry.

The H2 test DB uses `ddl-auto=create-drop`, so the new entity's schema is auto-generated in tests without a migration. A production Flyway migration can follow as a separate PR once this pattern is accepted.

Base / Stacking

Stacked on `feat/workflow-executor` (PR #21). CI won't exercise this branch until that base merges and this rebases onto `main`.

Test plan

• CI runs `./gradlew test` — 4 new + 22 existing WorkflowExecutorServiceTest cases should pass
• Reviewer: confirm 60s polling cadence is acceptable (if you want a faster wake-up, override `escalated.workflow.deferred-check-interval-seconds` in `application.properties`)
• Reviewer: sanity-check the `subList` usage in `executeParsed` — it creates a view, not a copy, which is fine here because Jackson only iterates once before the return