Migrate backend from Go to Quarkus (Java 21 / JAX-RS)

- Replaced Go stdlib server with Quarkus (RESTEasy Reactive + Jackson)
- 7 Java classes: Game POJO, GameService (JSON file I/O), 4 REST resources, static file serving
- Same JSON-per-game storage, same ZIP upload + bundle creation
- Same Svelte frontend (unchanged), built into the JAR via maven-resources-plugin
- Multi-stage Dockerfile: Node → Maven → JRE runtime

docker-compose.yml

@@ -8,7 +8,6 @@ services:
       - ./data:/data
     environment:
       - DOSTALGIA_DATA=/data
-      - PORT=8765
       # IGDB credentials (optional):
       # - TWITCH_CLIENT_ID=your_client_id
       # - TWITCH_CLIENT_SECRET=your_client_secret