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/options.go

@@ -0,0 +1,100 @@
+package slurm
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+)
+
+// ClientOption configures a Client via functional options.
+type ClientOption func(*clientConfig) error
+
+type clientConfig struct {
+	jwtKeyPath string
+	username   string
+	ttl        time.Duration
+	leeway     time.Duration
+	httpClient *http.Client
+}
+
+func defaultClientConfig() *clientConfig {
+	return &clientConfig{
+		ttl:    30 * time.Minute,
+		leeway: 30 * time.Second,
+	}
+}
+
+// WithJWTKey specifies the path to the JWT key file.
+func WithJWTKey(path string) ClientOption {
+	return func(c *clientConfig) error {
+		c.jwtKeyPath = path
+		return nil
+	}
+}
+
+// WithUsername specifies the Slurm username for JWT authentication.
+func WithUsername(username string) ClientOption {
+	return func(c *clientConfig) error {
+		c.username = username
+		return nil
+	}
+}
+
+// WithTokenTTL sets the JWT token time-to-live (default: 30 minutes).
+func WithTokenTTL(ttl time.Duration) ClientOption {
+	return func(c *clientConfig) error {
+		c.ttl = ttl
+		return nil
+	}
+}
+
+// WithTokenLeeway sets the JWT token refresh leeway (default: 30 seconds).
+func WithTokenLeeway(leeway time.Duration) ClientOption {
+	return func(c *clientConfig) error {
+		c.leeway = leeway
+		return nil
+	}
+}
+
+// WithHTTPClient specifies a custom HTTP client.
+func WithHTTPClient(client *http.Client) ClientOption {
+	return func(c *clientConfig) error {
+		c.httpClient = client
+		return nil
+	}
+}
+
+// NewClientWithOpts creates a new Slurm API client using functional options.
+// If WithJWTKey and WithUsername are provided, JWT authentication is configured
+// automatically. If no JWT options are provided, http.DefaultClient is used.
+func NewClientWithOpts(baseURL string, opts ...ClientOption) (*Client, error) {
+	cfg := defaultClientConfig()
+	for _, opt := range opts {
+		if err := opt(cfg); err != nil {
+			return nil, err
+		}
+	}
+
+	var httpClient *http.Client
+
+	if cfg.jwtKeyPath != "" && cfg.username != "" {
+		key, err := ReadJWTKey(cfg.jwtKeyPath)
+		if err != nil {
+			return nil, fmt.Errorf("read JWT key: %w", err)
+		}
+
+		transportOpts := []JWTTransportOption{
+			WithTTL(cfg.ttl),
+			WithLeeway(cfg.leeway),
+		}
+
+		tr := NewJWTAuthTransport(cfg.username, key, transportOpts...)
+		httpClient = tr.Client()
+	} else if cfg.httpClient != nil {
+		httpClient = cfg.httpClient
+	} else {
+		httpClient = http.DefaultClient
+	}
+
+	return NewClient(baseURL, httpClient)
+}