drpc: cap dshackle JVM heap with JAVA_OPTS=-Xms1g -Xmx4g

Image default is -Xms1024M with no -Xmx, so heap can grow unbounded (~30GiB).
us-41 was at 90% memory with no swap; -Xmx4g provides a safety limit.

Co-authored-by: Cursor <cursoragent@cursor.com>

drpc.yml

@@ -39,6 +39,8 @@ services:
     #  - "2449:2449"
     environment:
       DSHACKLE_LOG_LEVEL: ${DSHACKLE_LOG_LEVEL:-info}
+      # Cap JVM heap (image default is -Xms1024M with no -Xmx).
+      JAVA_OPTS: "-Xms1g -Xmx4g"
     labels:
       - "prometheus-scrape.enabled=true"
       - "prometheus-scrape.port=8081"