fix(minecraft): 3G heap so the server fits its 4 GB minimum

With MEMORY=4G and requiredMemoryMb 4096, Java's heap plus overhead
exceeded the container limit and the server was killed on start; the
boot test failed every time. With 3G it is ready in about 18s at 4 GB.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

games/minecraft-crossplay/game.yaml

@@ -31,7 +31,7 @@ defaultConfig:
   HARDCORE: false
   JVM_OPTS: -DgeyserTransport=nethernet -DgeyserAdvertiseAddresses={PUBLIC_IP}:{PUBLIC_PORT_19132}
   MAX_PLAYERS: 20
-  MEMORY: 4G
+  MEMORY: 3G
   MODE: survival
   MOTD: GBRHosting - {SERVER_NAME}
   ONLINE_MODE: true
@@ -117,8 +117,8 @@ configSchema:
       type: integer
     MEMORY:
       category: System & General
-      default: 4G
+      default: 3G
-      description: Maximum heap memory allocated to the Java process (e.g. 4G, 6G, 8G).
+      description: Java heap for the server. Keep it about 1 GB below your server's memory (3G on 4 GB, 7G on 8 GB); Java needs the rest, and a heap as large as the memory limit makes the server crash on start.
       title: Memory Allocation
       type: string
     MODE: