Add Docker Compose deployment with multi-stage build and nginx

Multi-stage Dockerfile builds the Vite app in Node 22 and serves static
assets from nginx:alpine. Includes gzip compression, SPA fallback routing,
immutable cache headers for hashed assets, and configurable port mapping
(default 8080). Deploy with `docker compose up -d`.

openspec/changes/docker-compose-deployment/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-03-01