monitoring: increase filesystem_filling_up prediction window to 24h

Reduces false positives from transient Nix store growth by basing the
linear prediction on a 24h trend instead of 6h.

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

services/monitoring/rules.yml

@@ -67,13 +67,13 @@ groups:
           summary: "Promtail service not running on {{ $labels.instance }}"
           description: "The promtail service has not been active on {{ $labels.instance }} for 5 minutes."
       - alert: filesystem_filling_up
-        expr: predict_linear(node_filesystem_free_bytes{mountpoint="/"}[6h], 24*3600) < 0
+        expr: predict_linear(node_filesystem_free_bytes{mountpoint="/"}[24h], 24*3600) < 0
         for: 1h
         labels:
           severity: warning
         annotations:
           summary: "Filesystem predicted to fill within 24h on {{ $labels.instance }}"
-          description: "Based on the last 6h trend, the root filesystem on {{ $labels.instance }} is predicted to run out of space within 24 hours."
+          description: "Based on the last 24h trend, the root filesystem on {{ $labels.instance }} is predicted to run out of space within 24 hours."
       - alert: systemd_not_running
         expr: node_systemd_system_running == 0
         for: 10m