feat: add SSE streaming endpoint for workflow events (#33)

- New internal/temporal/sse.go: StreamWorkflowEvents handler
- Polls Temporal GetWorkflowExecutionHistory every 2s
- Maps Temporal event types to semantic SSE events
  (activity_started/completed/failed, workflow_completed, etc.)
- Heartbeat every 15s, clean close on workflow completion
- Route: GET /workflow/stream?workflow_id=X&namespace=default
- Added stream resource to workflow ServiceAdapter spec

Closes #33

internal/serviceadapter/workflow_adapter.go

@@ -359,6 +359,19 @@ func GetWorkflowSpec() *Spec {
 					},
 				},
 			},
+			{
+				Name: "stream",
+				Methods: []Method{
+					{
+						Verb:         "GET",
+						UpstreamPath: "/workflow/stream",
+						Auth: &Auth{
+							Required:   true,
+							Capability: "workflow:read",
+						},
+					},
+				},
+			},
 		},
 	}
 }