feat(heartbeat): dead-man push to out-of-band Kuma every 5 min [#792]

HA curls status.knownelement.com push URL on a 5-min pattern; Kuma
pages the founder directly if heartbeats stop. Alert path independent
of HA itself.
https://projects.knownelement.com/issues/792

automations.yaml

@@ -688,3 +688,16 @@
       data:
         title: POST-DEPLOY VALIDATION FAILED
         message: "Missing/stale: {{ bad_list | join(', ') }}"
+- id: pfv_kuma_heartbeat
+  alias: PFV Kuma heartbeat (dead-man)
+  description: >
+    Pushes OK to the out-of-band Uptime Kuma every 5 minutes (#792).
+    Kuma pages the founder directly if heartbeats stop — the alert path
+    that works when HA itself is the failure.
+  mode: single
+  max_exceeded: silent
+  triggers:
+  - trigger: time_pattern
+    minutes: /5
+  actions:
+  - action: shell_command.kuma_ha_heartbeat