Upgrade Node.js to Version 22

This patch updates the Dockerfile to use Node.js 22 for running the
frontend. Given that the security support of Node.js 18 ends in 6 days
(30 Apr 2025), upgrading definitely makes sense.

Additionally, this also seems to fix the broken JSON generated by the
recently upgrraded version of @sveltejs/kit, thus fixing #584.

frontend/Dockerfile

@@ -1,5 +1,5 @@
 # Use this image as the platform to build the app
-FROM node:18-alpine AS external-website
+FROM node:22-alpine AS external-website
 
 # A small line inside the image to show who made it
 LABEL Developers="Sean Morley"
@@ -32,4 +32,4 @@ RUN chmod +x ./startup.sh
 USER node:node
 
 # Run startup.sh instead of the default command
-CMD ["./startup.sh"]
+CMD ["./startup.sh"]