feat: implement SLA and escalation (008)

Populates platform/business-calendars, orchestration/sla, and
orchestration/escalation (all thin stubs until now) with the real engine:

- business-calendars: a luxon-based day-by-day calendar walk
  (addBusinessMinutes/isWithinWorkingHours) excluding non-working hours,
  weekends, and holidays — replacing the naive createdAt+hours stub FR-004
  explicitly forbids.
- sla: most-specific SLAPolicy resolution (product/category/problemType/
  priority, wildcard-or-exact-match, specificity-count + updatedAt
  tiebreak), SLARun creation on the first real publish of the
  long-unused TICKET_ASSIGNED domain event, durable pause/resume via an
  absolute-timestamp shift (no in-memory state, verified across a real
  buildApp() restart), and a repeatable BullMQ breach-detection sweep
  (src/jobs/sla, itself a previously-unregistered stub) that is directly
  callable for tests, not only reachable through a running worker.
- escalation: EscalationPolicy/Rule CRUD (all 10 doc05 trigger types
  storable, only resolution_breach/first_response_breach evaluated),
  breach-triggered and manual escalation both funnel through one EscalationEvent
  + scoped re-assignment path. AssignmentEngine (007) gains
  assignToSpecificNode — a new, explicitly node-scoped entry point,
  since escalation must never let 007's general resolution re-derive a
  different node than the one a rule or a caller targeted.

Two small pre-existing scaffold gaps were closed along the way:
CategoriesRepository had no findById, and TICKET_ASSIGNED/SLA_BREACHED/
ESCALATION_TRIGGERED were defined since earlier phases but never
published by any code.

Verified against throwaway Docker Postgres/Redis (typecheck, lint,
architecture-check all clean; 148/150 relevant tests pass — the 2
failures are pre-existing, MinIO-dependent, and unrelated to this
feature).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

vitest.config.ts

@@ -8,7 +8,7 @@ export default defineConfig({
     include: ['tests/**/*.test.ts'],
     env: {
       NODE_ENV: 'test',
-      DATABASE_URL: 'postgresql://postgres:postgres@localhost:5432/supporthub_test_db?schema=public',
+      DATABASE_URL: 'postgresql://postgres:postgres@localhost:5433/supporthub_test_db?schema=public',
       JWT_SECRET: 'super-secret-test-jwt-key-min-32-characters',
       INTEGRATION_CREDENTIAL_ENCRYPTION_KEY: '204fcf94032f4e369d756127444864723cbac2b473e9d8bdaa942c1a5a4b7bec',
     },