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>

src/components/items/extraButtons.vue

@@ -8,7 +8,6 @@
 </template>
 
 <script>
-import arne from '../../arne.js'
 export default {
     data() {
         return {
@@ -47,7 +46,7 @@ export default {
             return new Promise((resolve, reject) => {
                 this.axios({
                     method: "get",
-                    url: `${arne.hostname}/music/reset`,
+                    url: `${window.__RUNTIME_CONFIG__.API_HOSTNAME}/music/reset`,
                 })
                     .then(() => {
                         resolve();
@@ -62,7 +61,7 @@ export default {
             return new Promise((resolve, reject) => {
                 this.axios({
                     method: "get",
-                    url: `${arne.hostname}/sync`,
+                    url: `${window.__RUNTIME_CONFIG__.API_HOSTNAME}/sync`,
                 })
                     .then(() => {
                         resolve();