fix(pd): add timeout and null-safety to getLeaderGrpcAddress()

The bolt RPC call in getLeaderGrpcAddress() returns null in Docker
bridge network mode, causing NPE when a follower PD node attempts
to discover the leader's gRPC address. This breaks store registration
and partition distribution when any node other than pd0 wins the
raft leader election.

Add a bounded timeout using the configured rpc-timeout, null-check
the RPC response, and fall back to deriving the address from the
raft endpoint IP when the RPC fails.

Closes #2959

Author: bitflicker64

hugegraph-pd/hg-pd-core/src/main/java/org/apache/hugegraph/pd/raft/RaftEngine.java

@@ -26,6 +26,8 @@
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
 
@@ -239,8 +241,20 @@ public String getLeaderGrpcAddress() throws ExecutionException, InterruptedExcep
             waitingForLeader(10000);
         }
 
-        return raftRpcClient.getGrpcAddress(raftNode.getLeaderId().getEndpoint().toString()).get()
-                            .getGrpcAddress();
+        try {
+            RaftRpcProcessor.GetMemberResponse response = raftRpcClient
+                    .getGrpcAddress(raftNode.getLeaderId().getEndpoint().toString())
+                    .get(config.getRpcTimeout(), TimeUnit.MILLISECONDS);
+            if (response != null && response.getGrpcAddress() != null) {
+                return response.getGrpcAddress();
+            }
+        } catch (TimeoutException | ExecutionException e) {
+            log.warn("Failed to get leader gRPC address via RPC, falling back to endpoint derivation", e);
+        }
+
+        // Fallback: derive from raft endpoint IP + local gRPC port (best effort)
+        String leaderIp = raftNode.getLeaderId().getEndpoint().getIp();
+        return leaderIp + ":" + config.getGrpcPort();
     }
 
     /**