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

src/main/resources/application.properties

@@ -0,0 +1,10 @@
+# ─── Server ──────────────────────────────────────
+quarkus.http.port=8765
+quarkus.http.host=0.0.0.0
+quarkus.http.cors=true
+
+# ─── Static resources (frontend SPA from META-INF/resources/) ──
+quarkus.http.static-resources.enable=true
+
+# ─── Data directory (game files, artwork) ────────
+dostalgia.data.dir=/data