E2E Testcontainers integration suite

Closes gap-analysis v2 §7.8 (no E2E vs live Postgres / §10.8
(Testcontainers opt-in suite).

- tests/e2e/transactionLifecycle.e2e.test.ts — Postgres-backed E2E
  suite via @testcontainers/postgresql. Brings up a real postgres:15
  container, applies schema.sql (via pg simple-query protocol so $$
  function bodies survive) + migrations 002/003/004, wires the
  plans endpoints against it, and asserts:
    * POST /api/plans persists and reads back
    * eventBus.publish produces a hash-chained pair with verifyChain
      returning ok
    * idempotency_keys row insertion round-trips
- jest.e2e.config.js — dedicated config for tests/e2e/ with 120s
  timeout; default jest.config.js now ignores /e2e/ so `npm test`
  stays fast (<5s) and doesn't require Docker.
- package.json — adds 'npm run test:e2e' (sets RUN_E2E=1).
- devDependencies — testcontainers + @testcontainers/postgresql.
- Suite gates on `RUN_E2E=1`. Without it the describe block is
  skipped, so CI environments without Docker don't fail; a guard
  test asserts the skip invariant.
- .github/workflows/ci.yml — adds orchestrator-test (tsc + jest)
  and orchestrator-e2e (gated on the 'run-e2e' PR label or any
  push to main).
- Verification:
    npx tsc --noEmit              clean
    npm test (unit)               7 suites, 80/80 passing
    npm run test:e2e              1 suite, 4/4 passing (docker up)

orchestrator/package.json

@@ -8,6 +8,7 @@
     "dev": "ts-node src/index.ts",
     "start": "node dist/index.js",
     "test": "jest",
+    "test:e2e": "RUN_E2E=1 jest --config=jest.e2e.config.js",
     "migrate": "ts-node src/db/migrations/index.ts"
   },
   "dependencies": {
@@ -27,6 +28,7 @@
   },
   "devDependencies": {
     "@jest/globals": "^30.3.0",
+    "@testcontainers/postgresql": "^11.14.0",
     "@types/cors": "^2.8.17",
     "@types/express": "^4.17.21",
     "@types/jest": "^30.0.0",
@@ -36,6 +38,7 @@
     "@types/uuid": "^9.0.6",
     "jest": "^30.3.0",
     "supertest": "^7.2.2",
+    "testcontainers": "^11.14.0",
     "ts-jest": "^29.4.9",
     "ts-node": "^10.9.2",
     "typescript": "^5.3.3"