feat: Add heartbeat phone-home script and norn SSH key

- parahub-heartbeat: cURL heartbeat to cloud API every 5min via cron
- authorized_keys: add norn@parahub-ng for WiFi password SSH retrieval
- 99-parahub-mesh: section 12 enables cron + heartbeat on first boot

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

files/usr/bin/parahub-heartbeat

@@ -0,0 +1,31 @@
+#!/bin/sh
+# Phone-home heartbeat to Parahub cloud via Yggdrasil
+PARAHUB_API="http://[200:abb9:5810:37d3:8a4c:98a6:b82b:969a]/api/v1/iot/mesh/heartbeat"
+HEARTBEAT_KEY="IqPosrcpTQKSbLHxOG3iLTl_K2MsDxvd"
+
+# Check Yggdrasil connectivity first
+ping6 -c 1 -W 3 200:abb9:5810:37d3:8a4c:98a6:b82b:969a >/dev/null 2>&1 || exit 0
+
+# Read identity from /etc/parahub/keys
+. /etc/parahub/keys 2>/dev/null
+MAC="${NODE_MAC:-$(cat /sys/class/net/br-lan/address 2>/dev/null)}"
+HOSTNAME="$(uci -q get system.@system[0].hostname)"
+YGG_ADDR="${YGGDRASIL_ADDRESS:-unknown}"
+SSID="${PRIVATE_SSID:-unknown}"
+UPTIME="$(cut -d. -f1 /proc/uptime)"
+
+# Detect hardware from board_name
+HW=$(cat /tmp/sysinfo/board_name 2>/dev/null)
+case "$HW" in
+    glinet,gl-axt1800) HW="axt1800" ;;
+    glinet,gl-mt3000) HW="mt3000" ;;
+    glinet,gl-mt6000) HW="mt6000" ;;
+    asus,rt-ax53u) HW="ax53u" ;;
+    *) HW="${HW:-unknown}" ;;
+esac
+
+curl -s -m 10 -X POST \
+    -H "Content-Type: application/json" \
+    -H "Authorization: Bearer ${HEARTBEAT_KEY}" \
+    -d "{\"mac\":\"${MAC}\",\"hostname\":\"${HOSTNAME}\",\"yggdrasil_address\":\"${YGG_ADDR}\",\"firmware_version\":\"25.12.0-rc4\",\"hardware_profile\":\"${HW}\",\"uptime\":${UPTIME},\"private_ssid\":\"${SSID}\"}" \
+    "${PARAHUB_API}" >/dev/null 2>&1