ha: add universal media-partition low-space guard for Frigate

Adds a command_line sensor (HAOS Media Partition Free, df of /media =
sda8) and an automation that stops the Frigate add-on when free space
drops below 50 GB for 2 min. Protects HAOS Core from the VAULT1 CIFS
fallthrough fill scenario (RB-001). Fires regardless of CIFS mount
state — the mount sensor can be stale during the crisis. Stop-only +
max-priority ntfy alert; no auto-remount (needs admin token).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ha/automations.yaml

@@ -78,3 +78,29 @@
         See RB-001 in runbooks/phase5-incident-log.md for recovery steps.
       priority: high
       tags: warning,house
+
+- id: frigate_disk_guard_stop
+  alias: Frigate Disk Guard – Stop Frigate when media partition low
+  description: >-
+    Universal low-space safety net. If the HAOS /media (sda8) partition free
+    space drops below threshold, stop the Frigate add-on so it can't fill the
+    system partition and take Core down. Fires regardless of VAULT1 CIFS state
+    (the mount sensor can be stale during exactly this crisis).
+  triggers:
+  - platform: numeric_state
+    entity_id: sensor.haos_media_partition_free
+    below: 50            # GB free — tune to taste
+    for: "00:02:00"
+  actions:
+  - action: hassio.addon_stop
+    data:
+      addon: ccab4aaf_frigate-fa     # confirm slug: Settings → Add-ons → Frigate → URL
+  - action: rest_command.ntfy_grafana_alerts
+    data:
+      title: "Frigate STOPPED – HAOS media partition low"
+      message: >-
+        Only {{ states('sensor.haos_media_partition_free') }} GB free on /media
+        (sda8). Frigate add-on stopped to protect the system partition. Check
+        whether VAULT1 CIFS dropped (RB-001), clear space, then restart Frigate.
+      priority: max
+      tags: rotating_light,house