fix(slurm): add default 30s timeout to HTTP client

Replaces http.DefaultClient with a client that has a 30s timeout to prevent indefinite hangs when the Slurm REST API is unresponsive.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/slurm/options_test.go

@@ -2,7 +2,6 @@ package slurm
 
 import (
 	"crypto/rand"
-	"net/http"
 	"os"
 	"path/filepath"
 	"testing"
@@ -61,8 +60,8 @@ func TestNewClientWithOpts_BackwardCompatible(t *testing.T) {
 	if client == nil {
 		t.Fatal("expected non-nil client")
 	}
-	if client.client != http.DefaultClient {
-		t.Error("expected http.DefaultClient when no options provided")
+	if client.client.Timeout != DefaultTimeout {
+		t.Errorf("expected Timeout=%v, got %v", DefaultTimeout, client.client.Timeout)
 	}
 }