fix: workflow dispatcher uses internal handler instead of raw gRPC proxy

- Wire WorkflowAdapter as internal handler (JSON-to-gRPC bridge)
- Add ServeHTTP to WorkflowAdapter: maps X-Resource to Temporal action
- Rename resource 'start' to 'execute' for consistency
- Add GET methods for describe/list/history resources
- Remove unused workflowAdapterImpl variable
- SDK clients can now send JSON, gateway translates to gRPC

cmd/gateway/main.go

@@ -76,9 +76,11 @@ func main() {
 	
 	// Add workflow service adapter (uses Temporal handler for gRPC forwarding)
 	workflowSpec := serviceadapter.GetWorkflowSpec()
+	workflowAdapterHandler := serviceadapter.NewWorkflowAdapter(temporalHandler)
 	workflowAdapter := &serviceadapter.ServiceAdapter{
 		Namespace:   "temporal",
 		ServiceName: "workflow",
+		Handler:     workflowAdapterHandler,
 		Spec:        *workflowSpec,
 	}
 	_ = registry.Add(workflowAdapter)
@@ -120,8 +122,7 @@ func main() {
 	dispatcher := serviceadapter.NewDispatcher(registry, jwtValidator)
 	
 	// Wire workflow adapter to temporal handler for proper request forwarding
-	workflowAdapterImpl := serviceadapter.NewWorkflowAdapter(temporalHandler)
-	_ = workflowAdapterImpl // The dispatcher will call temporal handler directly for gRPC
+	// workflowAdapterHandler (above) handles JSON-to-gRPC translation for workflow service
 
 	// Create router that handles health endpoints, X-Service (ServiceAdapter) routing,
 	// temporal endpoints, and passes others to upstream handler