Count flows rather than nodes in the health report

is keyed by node id, so a four-node flow reported four flows.

backend/app/api/routes/utils.py

@@ -69,7 +69,9 @@ async def health(request: Request, response: Response) -> dict[str, Any]:
             redis_info["rtt_ms"] = round((time.perf_counter() - start) * 1000, 1)
             if not connected:
                 problems.append("redis unreachable")
-        engine["flows"] = len(getattr(controller, "loaded", {}) or {})
+        # `loaded` is keyed by node id, so its length is a node count.
+        loaded = getattr(controller, "loaded", {}) or {}
+        engine["flows"] = len({entry.flow for entry in loaded.values()})
         engine["nodes"] = len(
             getattr(getattr(controller, "pipeline", None), "nodes", []) or []
         )