feat(sdlc): staging environment + automated staging→prod pipeline

- pr-checks.yml: PR gate — frontend typecheck+jest, backend import smoke,
  image builds (no push), Claude AI review posted as PR comment (severe
  findings block merge)
- deploy.yml (replaces build-and-push.yml): merge to main builds+pushes
  images tagged sha-<sha>/staging, deploys the staging Portainer stack via
  webhook, runs Playwright E2E journeys against staging, then retags the
  verified images :prod (previous kept as :prod-previous) and deploys prod
- docker-compose.portainer.staging.yml: second Portainer stack — :staging
  images, sc_staging_* names, own macvlan IPs, Airflow on 8081; data
  bootstrapped from source via the staging Airflow DAGs
- prod compose now pins :prod instead of :latest (only the promotion step
  moves it; :latest is no longer published)
- e2e/: 6 Playwright journeys (search, postcode, detail, compare, rankings)
  driven by BASE_URL — the promotion gate
- scripts/ci/ai_review.py: Claude review with structured JSON findings
- docs/DEPLOY.md: full SDLC doc incl. one-time setup checklist and rollback
- replaced removed 'next lint' with tsc typecheck; fixed stale jest tests
  (slug URLs, N/A formatting, stable trend, fake-timer setup)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PqGhF93UrpDNvXBLMjJENL

docker-compose.portainer.yml

@@ -36,7 +36,7 @@ services:
 
   # ── FastAPI Backend ───────────────────────────────────────────────────
   backend:
-    image: privaterepo.sitaru.org/tudor/school_compare-backend:latest
+    image: privaterepo.sitaru.org/tudor/school_compare-backend:prod
     container_name: schoolcompare_backend
     environment:
       DATABASE_URL: postgresql://${DB_USERNAME}:${DB_PASSWORD}@sc_database:5432/${DB_DATABASE_NAME}
@@ -59,7 +59,7 @@ services:
 
   # ── Next.js Frontend ──────────────────────────────────────────────────
   frontend:
-    image: privaterepo.sitaru.org/tudor/school_compare-frontend:latest
+    image: privaterepo.sitaru.org/tudor/school_compare-frontend:prod
     container_name: schoolcompare_nextjs
     environment:
       - NODE_ENV=production
@@ -103,7 +103,7 @@ services:
 
   # ── Airflow API Server + UI ───────────────────────────────────────────
   airflow-api-server:
-    image: privaterepo.sitaru.org/tudor/school_compare-pipeline:latest
+    image: privaterepo.sitaru.org/tudor/school_compare-pipeline:prod
     container_name: schoolcompare_airflow_api
     command: airflow api-server --port 8080
     ports:
@@ -142,7 +142,7 @@ services:
 
   # ── Airflow Scheduler ──────────────────────────────────────────────
   airflow-scheduler:
-    image: privaterepo.sitaru.org/tudor/school_compare-pipeline:latest
+    image: privaterepo.sitaru.org/tudor/school_compare-pipeline:prod
     container_name: schoolcompare_airflow_scheduler
     command: airflow scheduler
     environment:
@@ -172,7 +172,7 @@ services:
 
   # ── Airflow DB Init (one-shot) ───────────────────────────────────────
   airflow-init:
-    image: privaterepo.sitaru.org/tudor/school_compare-pipeline:latest
+    image: privaterepo.sitaru.org/tudor/school_compare-pipeline:prod
     container_name: schoolcompare_airflow_init
     command: bash -c "airflow db migrate && airflow dags delete school_data_daily -y 2>/dev/null; airflow dags delete school_data_monthly_ofsted -y 2>/dev/null; airflow dags delete school_data_annual_ees -y 2>/dev/null; airflow dags reserialize"
     environment: