Ignore non-SLO probe bookkeeping in bottleneck diagnosis

src/aituner/harness.py

@@ -341,6 +341,8 @@ def _active_bottleneck(probe: dict[str, Any] | None) -> str:
         and not str(k).startswith("tpot")
         and not str(k).startswith("probe_elapsed_s>")
     )
+    if ttft_count == 0 and tpot_count == 0 and request_failed_count == 0:
+        return "none_obvious"
     if ttft_count >= max(tpot_count, request_failed_count):
         return "ttft_prefill"
     if tpot_count >= max(ttft_count, request_failed_count):