Harden admin hash env contract for Docker and CI

[IgnazioDS]

Summary

• support ADMIN_UI_PASSWORD_HASH_B64 in admin server config with fallback to ADMIN_UI_PASSWORD_HASH
• switch Docker/CI admin env wiring to the base64 hash variant to avoid Compose interpolation pitfalls
• update release checklist and docs for the new env contract
• refactor make docker-build to use a dedicated script wrapper

Validation

• cd apps/admin && npm run build
• make demo-up
• API_URL=http://127.0.0.1:8000 ADMIN_UI_URL=http://127.0.0.1:3000 ADMIN_TOKEN=dev-admin-token ADMIN_UI_USERNAME=admin ADMIN_UI_PASSWORD=admin123! ./scripts/smoke_test_admin.sh
• make release-check

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