feat(client): add functional option pattern for JWT auth config

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

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

internal/slurm/slurm.go

@@ -3,7 +3,7 @@
 // The client handles authentication via X-SLURM-USER-NAME and X-SLURM-USER-TOKEN
 // headers, request/response marshaling, and error handling.
 //
-// Basic usage:
+// Static token authentication:
 //
 //	httpClient := &http.Client{
 //		Transport: &slurm.TokenAuthTransport{
@@ -15,4 +15,14 @@
 //	if err != nil {
 //		log.Fatal(err)
 //	}
+//
+// JWT authentication (auto-signed from local key):
+//
+//	client, err := slurm.NewClientWithOpts("http://localhost:6820",
+//		slurm.WithJWTKey("/etc/slurm/jwt/slurm_jwt.key"),
+//		slurm.WithUsername("slurmapi"),
+//	)
+//	if err != nil {
+//		log.Fatal(err)
+//	}
 package slurm