Add Docker support with runtime environment variable configuration

- Remove temporary arne.js file
- Add runtime configuration via window.__RUNTIME_CONFIG__
- Create public/config.template.js for hostname injection
- Add Dockerfile with multi-stage build (node + nginx)
- Add docker-entrypoint.sh to generate config.js at startup
- Add .dockerignore
- Update all components to use runtime config instead of arne.js
- Update index.html to load config.js before app

This allows deploying the same Docker image to different environments
by setting the API_HOSTNAME environment variable at runtime.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

docker-entrypoint.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+set -e
+
+# Generate config.js from template at runtime
+envsubst < /usr/share/nginx/html/config.template.js > /usr/share/nginx/html/config.js
+
+# Start nginx
+exec "$@"