feat: generic ping_monitor thresholds; round RTT to nearest ms

- threshold.py: add _find_threshold() with suffix fallback so thresholds
  like ping_monitor.rtt_avg match ping_monitor.8_8_8_8_rtt_avg etc.;
  each pinged host keeps its own alert state
- hbdclass.py: format RTT as integer ms (round())
- live.html: JS RTT display rounded to nearest ms (Math.round)

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

hbd/server/threshold.py

@@ -803,6 +803,29 @@ class ThresholdChecker:
             self._check_pending_or_renotify(host_name, alert_state, metric_path, value, threshold, None)
 
         return None
+    def _find_threshold(
+        self, thresholds: Dict[str, "ThresholdConfig"], metric_path: str
+    ) -> Optional["ThresholdConfig"]:
+        """Return the threshold for *metric_path*, falling back to suffix matches.
+
+        Allows generic thresholds like ``ping_monitor.rtt_avg`` to match
+        fully-qualified paths like ``ping_monitor.8_8_8_8_rtt_avg``.
+        The exact match is always tried first; then successive leading
+        underscore-delimited segments are stripped from the field name until
+        a match is found or no segments remain.
+        """
+        if metric_path in thresholds:
+            return thresholds[metric_path]
+        plugin, sep, field = metric_path.partition(".")
+        if not sep:
+            return None
+        parts = field.split("_")
+        for i in range(1, len(parts)):
+            candidate = plugin + "." + "_".join(parts[i:])
+            if candidate in thresholds:
+                return thresholds[candidate]
+        return None
+
     def check_plugin_data(
         self,
         host_name: str,
@@ -831,11 +854,10 @@ class ThresholdChecker:
         for metric_name, value in data.items():
             metric_path = f"{plugin_name}.{metric_name}"
             
-            if metric_path not in thresholds:
+            threshold = self._find_threshold(thresholds, metric_path)
+            if threshold is None:
                 continue
             
-            threshold = thresholds[metric_path]
-            
             # Get or create alert state
             if metric_path not in alert_states:
                 alert_states[metric_path] = AlertState(metric_path)