fix(node-agent): unique event IDs per service to prevent same-second overwrites

Multiple service_healthy (or containers_not_running) events emitted in the
same second for different containers shared the same filename pattern
evt-{node}-{ts}-{type}.json — the second write silently overwrote the first,
so the observer only ever saw the last container checked per event type per cycle.

Fix: include a sanitized service name slug in the ID so every event gets a
unique file, e.g. evt-vps-1234-service_healthy-node-agent.json.

Also adds import re (required for re.sub in the slug generation).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/node-agent/src/node_agent.py

@@ -27,6 +27,7 @@ NEVER TOUCHED on any node:
 import json
 import logging
 import os
+import re
 import shutil
 import socket
 import subprocess
@@ -153,7 +154,11 @@ class NodeAgent:
     def emit_event(self, event_type: str, severity: str, service,
                    message: str, payload: dict = None):
         ts = int(time.time())
-        event_id = f"evt-{self.node_name}-{ts}-{event_type}"
+        # Include service slug in the ID so that multiple events of the same type
+        # emitted within the same second (e.g. service_healthy for N containers)
+        # don't overwrite each other — each gets a unique filename.
+        svc_slug = re.sub(r"[^a-z0-9]", "-", (service or "node").lower())[:32].strip("-")
+        event_id = f"evt-{self.node_name}-{ts}-{event_type}-{svc_slug}"
         event = {
             "id":        event_id,
             "timestamp": ts,