fix: tighten datasource trigger guards

backend/app/services/scheduler.py

@@ -274,6 +274,11 @@ def run_collector_now(collector_name: str) -> bool:
         logger.error("Collector not found: %s", collector_name)
         return False
 
+    existing_task = get_running_collector_task(collector_name)
+    if existing_task is not None and not existing_task.done():
+        logger.warning("Collector %s is already running in-memory; skipping duplicate trigger", collector_name)
+        return False
+
     try:
         task = asyncio.create_task(run_collector_task(collector_name), name=_collector_task_name(collector_name))
         RUNNING_COLLECTOR_TASKS[collector_name] = task