feat(infra): add launch readiness quick wins

- Add mem_limit to all 6 app containers (db: 512m, redis: 128m,
  api: 512m, celery-worker: 512m, celery-beat: 128m, flower: 128m)
- Restrict Flower port to localhost (127.0.0.1:5555:5555)
- Add PostgreSQL and Redis health checks to /health/ready endpoint
  with individual check details (name, status, latency)
- Add scaling guide with metrics, thresholds, Hetzner pricing
- Add server verification script (12 infrastructure checks)
- Update hetzner-server-setup.md with progress and pending tasks

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

mkdocs.yml

@@ -214,6 +214,7 @@ nav:
       - CloudFlare Setup: deployment/cloudflare.md
       - Gitea CI/CD: deployment/gitea.md
       - Hetzner Server Setup: deployment/hetzner-server-setup.md
+      - Scaling Guide: deployment/scaling-guide.md
       - Environment Variables: deployment/environment.md
       - Incident Response: deployment/incident-response.md
       - Stripe Integration: deployment/stripe-integration.md
@@ -235,6 +236,7 @@ nav:
       - Permissions Plan: proposals/plan-perms.md
       - Validator Noqa & Remaining Findings: proposals/validator-noqa-suppressions-and-remaining-findings.md
       - Backward Compatibility Cleanup: proposals/backward-compatibility-cleanup.md
+      - Fix SEC-015 x-html Findings: proposals/fix-1600-sec015-xhtml-findings.md
 
     # --- Archive ---
     - Archive: