canbus: presence layer + departure failsafes

Water heater = occupancy truth. New Pi package campsite_presence.yaml:
rv_occupied + phones_on_campsite_wifi template sensors (wifi one stays
unavailable until the MikroTik integration lands — load-bearing for the
dead-man trigger), MQTT bridging home, a local notify-only dead-man
(heater on, no phones on WiFi 3h), and disabled pre-staged lot-light
automations for the future shed Shelly.

dsi_fault_alert.yaml gains the Octavia MQTT relay (campsite/octavia/say)
so home HA — which has no file access — can speak through the verified
webhook path.

Home-side (UI-managed, not in repo): quick failsafe (both out of the
enlarged 150m campsite zone 25 min → fans/lights off + summary ping) and
heater failsafe (2h → heater off with bridge round-trip confirmation).
Both verified live; fan states snapshot-restored after the test.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

canbus/ha/dsi_fault_alert.yaml

@@ -28,6 +28,25 @@ rest_command:
        "allowed_mentions": {"users": ["321798967669030912"]}}
 
 automation:
+  # --- Octavia relay: anything on the broker can speak through the one
+  # verified webhook path. Home HA's failsafe automations publish here
+  # (campsite/octavia/say, payload = the message) since home has no
+  # file/packages access for its own rest_command. ---
+  - id: campsite_octavia_relay
+    alias: "Octavia: MQTT relay"
+    triggers:
+      - trigger: mqtt
+        topic: "campsite/octavia/say"
+    conditions:
+      - condition: template
+        value_template: "{{ trigger.payload | length > 0 and trigger.payload | length < 1900 }}"
+    actions:
+      - action: rest_command.discord_server_alerts
+        data:
+          message: "{{ trigger.payload }}"
+    mode: queued
+    max: 5
+
   - id: camper_dsi_fault_discord
     alias: "Camper: DSI fault → Discord"
     description: >-