canbus: furnace + water-heater status sensors (running + DSI fault)

Decode node 89 (furnace) read-only: Furnace Running (page-3 b0 bit0) and
Furnace DSI Fault (b0 bit5), same type-0x1E DSI encoding as the water
heater. The furnace is thermostat-controlled, not a Lippert load — it
sits on the bus only to report ignition state. Captures only ever showed
0x80 (off), so the 0x81 running / 0xA0 fault bytes are inferred by
parallel to node 95; confirm on the first real burn.

Add Water Heater Heating (node 95 page-3 x[3] bit7 = burner actively
firing) — distinct from the on/off switch, which only reflects "enabled".

Carry all three through the MQTT bridge to home HA, add the furnace
DSI-fault Octavia alert mirroring the water heater, and update the README
node map (89 was "unknown switched load"). Campsite + home Camper
dashboards updated live.

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

canbus/ha/dsi_fault_alert.yaml

@@ -83,3 +83,44 @@ automation:
             averted. Try to remember this feeling next time you eyeball the
             tank gauge and say "eh, it's fine."
     mode: single
+
+  # --- Furnace DSI fault (node 89). Same lockout scheme as the water heater
+  # (page-3 b0 bit5); see canbus/README.md. A furnace lockout means no forced-air
+  # heat — more urgent than the water heater on a cold night. ---
+  - id: camper_furnace_dsi_fault_discord
+    alias: "Camper: Furnace DSI fault → Discord"
+    description: >-
+      10s 'for' debounces a single glitched broadcast frame; a real lockout
+      is latched by the module so it easily survives the wait.
+    triggers:
+      - trigger: state
+        entity_id: binary_sensor.onecontrol_can_furnace_dsi_fault
+        to: "on"
+        for: "00:00:10"
+    actions:
+      - action: rest_command.discord_server_alerts
+        data:
+          message: >-
+            <@321798967669030912> 🥶 **FURNACE DSI FAULT** — the furnace tried to
+            light and gave up. That means no heat. Same usual suspect: you're out
+            of propane (or the igniter died, but c'mon). It's in lockout — swap the
+            tank, then cycle the thermostat to relight before everything inside
+            hits ambient.
+    mode: single
+
+  - id: camper_furnace_dsi_fault_cleared_discord
+    alias: "Camper: Furnace DSI fault cleared → Discord"
+    triggers:
+      - trigger: state
+        entity_id: binary_sensor.onecontrol_can_furnace_dsi_fault
+        from: "on"
+        to: "off"
+        for: "00:00:10"
+    actions:
+      - action: rest_command.discord_server_alerts
+        data:
+          message: >-
+            ✅ Furnace fault cleared — it's lighting again and making heat. Enjoy
+            the warmth, and maybe glance at the propane gauge once in a while like
+            a functioning adult.
+    mode: single