fix: reschedule APScheduler job immediately when status check interval is updated

Interval was read once at startup — changing it via API had no effect
until server restart. Now calls reschedule_status_checks() after saving.

backend/app/api/routes/scan.py

@@ -8,6 +8,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.api.deps import get_current_user
 from app.core.config import settings
+from app.core.scheduler import reschedule_status_checks
 from app.db.database import AsyncSessionLocal, get_db
 from app.db.models import Node, PendingDevice, ScanRun
 from app.schemas.nodes import NodeCreate
@@ -110,6 +111,7 @@ async def update_scan_config(payload: ScanConfig, _: str = Depends(get_current_u
     try:
         settings.scanner_ranges = payload.ranges
         settings.save_overrides()
+        reschedule_status_checks(payload.interval_seconds)
         return payload
     except Exception as exc:
         raise HTTPException(status_code=500, detail=str(exc)) from exc

backend/app/core/scheduler.py

@@ -53,5 +53,11 @@ def start_scheduler() -> None:
     logger.info("Scheduler started — status checks every %ds", settings.status_checker_interval)
 
 
+def reschedule_status_checks(interval_seconds: int) -> None:
+    """Update the status check interval on the running scheduler."""
+    scheduler.reschedule_job("status_checks", trigger="interval", seconds=interval_seconds)
+    logger.info("Status checks rescheduled to every %ds", interval_seconds)
+
+
 def stop_scheduler() -> None:
     scheduler.shutdown(wait=False)