Feat: Add production-grade multi-stage container image for UI
Two-stage build (node:22-slim builder + nginxinc/nginx-unprivileged:alpine
runtime) with SPA fallback routing, long-lived cache headers for fingerprinted
assets, non-root user (UID 101), and no Node.js toolchain in runtime image
(82 MB vs 329 MB+ single-stage). Verified by ui/tests/build/verify_production_image.sh
covering build, health, SPA routing, non-root, stdout logging, cache-control
headers, SIGTERM exit 0, Node.js absent, secret-free layers, and dep-layer
cache hit. 102 integration tests still pass; shellcheck clean.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
agatha
1b3468b72d