Add Dockerfile and compose setup for self-hosting

Multi-stage build: Node builds the static PWA, nginx serves it with an SPA
fallback, long-lived caching for hashed assets, no-cache for the app shell
and service worker, and the correct type for the web manifest.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VsorPV3JeJRoZ1mD1pdvtL

docker/nginx.conf

@@ -0,0 +1,33 @@
+server {
+	listen 80;
+	server_name _;
+	root /usr/share/nginx/html;
+
+	gzip on;
+	gzip_types text/css application/javascript application/json application/manifest+json image/svg+xml;
+
+	# Hashed build output never changes.
+	location /_app/immutable/ {
+		add_header Cache-Control "public, max-age=31536000, immutable";
+		try_files $uri =404;
+	}
+
+	# The service worker and app shell must be re-checked so updates reach clients.
+	location = /service-worker.js {
+		add_header Cache-Control "no-cache";
+		try_files $uri =404;
+	}
+
+	# nginx's default MIME table has no entry for the PWA manifest.
+	location ~ \.webmanifest$ {
+		types { }
+		default_type application/manifest+json;
+		add_header Cache-Control "no-cache";
+	}
+
+	# Client-side app: unknown paths fall back to the SPA shell.
+	location / {
+		add_header Cache-Control "no-cache";
+		try_files $uri $uri/ /index.html;
+	}
+}