Fix docker development:

- Specify elixir version (1.15) in Dockerfile base image

- Add npm package to Dockerfile

- Fix vite server unreachable from outside the docker container:
  issue https://framagit.org/framasoft/mobilizon/-/issues/1225

vite.config.js

@@ -83,6 +83,9 @@ export default defineConfig(({ command }) => {
   return {
     plugins,
     build,
+    server: {
+      host: isDev ? "0.0.0.0" : "localhost",
+    },
     resolve: {
       alias: {
         "@": path.resolve(__dirname, "./src"),