Add Temporal worker and test client programs

Creates:
- cmd/worker/main.go: Worker that registers workflows and activities
- cmd/test-workflow/main.go: Test client to trigger workflows

Adds go.temporal.io/sdk dependency to go.mod.

internal/workflow/worker.go

@@ -0,0 +1,120 @@
+package workflow
+
+import (
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"go.temporal.io/sdk/client"
+	"go.temporal.io/sdk/worker"
+	"go.temporal.io/sdk/temporal"
+	"go.temporal.io/sdk/workflow"
+)
+
+// WorkerConfig holds worker configuration
+type WorkerConfig struct {
+	HostPort  string
+	Namespace string
+	TaskQueue string
+}
+
+// NewWorker creates and starts a Temporal worker
+func NewWorker(cfg WorkerConfig) error {
+	// Connect to Temporal server
+	c, err := client.Dial(client.Options{
+		HostPort:  cfg.HostPort,
+		Namespace: cfg.Namespace,
+	})
+	if err != nil {
+		return err
+	}
+	defer c.Close()
+
+	log.Printf("Connected to Temporal at %s (namespace: %s)", cfg.HostPort, cfg.Namespace)
+
+	// Create worker
+	w := worker.New(c, cfg.TaskQueue, worker.Options{})
+
+	// Register workflows
+	w.RegisterWorkflow(HelloWorldWorkflow)
+	w.RegisterWorkflow(GreeterWorkflow)
+	w.RegisterWorkflow(ProcessOrderWorkflow)
+
+	// Register activities
+	w.RegisterActivity(GreetActivity)
+	w.RegisterActivity(ValidateOrderActivity)
+	w.RegisterActivity(ProcessPaymentActivity)
+	w.RegisterActivity(NotifyCustomerActivity)
+
+	// Start worker (blocks until signal received)
+	log.Printf("Starting worker on task queue: %s", cfg.TaskQueue)
+
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
+
+	go func() {
+		if err := w.Run(worker.InterruptCh()); err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	// Wait for shutdown signal
+	<-sigChan
+	log.Println("Shutting down worker...")
+	w.Stop()
+
+	return nil
+}
+
+// ProcessOrderWorkflow demonstrates multi-step workflow with activities
+func ProcessOrderWorkflow(ctx workflow.Context, orderID string) (string, error) {
+	opts := workflow.ActivityOptions{
+		StartToCloseTimeout: 5 * time.Minute,
+		RetryPolicy: &temporal.RetryPolicy{
+			InitialInterval:    time.Second,
+			BackoffCoefficient: 2.0,
+			MaximumInterval:    time.Minute,
+			MaximumAttempts:    3,
+		},
+	}
+	ctx = workflow.WithActivityOptions(ctx, opts)
+
+	// Step 1: Validate order
+	var validated bool
+	if err := workflow.ExecuteActivity(ctx, ValidateOrderActivity, orderID).Get(ctx, &validated); err != nil {
+		return "", err
+	}
+	if !validated {
+		return "", temporal.NewApplicationError("invalid order", "InvalidOrder")
+	}
+
+	// Step 2: Process payment
+	var paymentID string
+	if err := workflow.ExecuteActivity(ctx, ProcessPaymentActivity, orderID).Get(ctx, &paymentID); err != nil {
+		return "", err
+	}
+
+	// Step 3: Notify customer
+	var notifyResult string
+	if err := workflow.ExecuteActivity(ctx, NotifyCustomerActivity, orderID).Get(ctx, &notifyResult); err != nil {
+		return "", err
+	}
+
+	return paymentID, nil
+}
+
+// GreeterWorkflow is a multi-step workflow
+func GreeterWorkflow(ctx workflow.Context, name string) (string, error) {
+	opts := workflow.ActivityOptions{
+		StartToCloseTimeout: 5 * time.Minute,
+	}
+	ctx = workflow.WithActivityOptions(ctx, opts)
+
+	var result string
+	if err := workflow.ExecuteActivity(ctx, GreetActivity, name).Get(ctx, &result); err != nil {
+		return "", err
+	}
+	return result, nil
+}