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/temporal/handler.go

@@ -67,6 +67,8 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		h.handleHealth(w, r)
 	case "/workflow/metrics":
 		h.handleMetrics(w, r)
+	case "/workflow/stream":
+		h.StreamWorkflowEvents(w, r)
 	default:
 		w.WriteHeader(http.StatusNotFound)
 		h.writeError(w, "", "NOT_FOUND", "Endpoint not found")