feat(sensors): sysfs thermal fallback + SBC fleet coverage [#341][#457][#458]

lm-sensors is silent on SBCs (Pis, Jetson-class), so the wrapper now falls
back to /sys/class/thermal zones rendered in lm-sensors format when native
sensors output is empty; suppressed when native output exists to avoid
duplicates. TDD: 3 new unit tests (12 green). Sensor stack deployed to
jetson + pfvsvrpi + 3 subopis (verified from poller), HA pack extended to
16 sensors across 14 hosts, high-temp automation covers the SBC fleet.

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

dcinfra/sensors/temper/lmsensors-extend.sh

@@ -14,6 +14,7 @@ set -euo pipefail
 
 VENV_PY="${VENV_PY:-/opt/temper-venv/bin/python}"
 NATIVE_SENSORS_BIN="${NATIVE_SENSORS_BIN:-/usr/bin/sensors}"
+SYSFS_THERMAL_ROOT="${SYSFS_THERMAL_ROOT:-/sys/class/thermal}"
 CHIP_NAME="${CHIP_NAME:-temper-usb-1}"
 
 # Render lm-sensors format block from internal/external Celsius values.
@@ -71,10 +72,41 @@ run_native_sensors() {
     "$NATIVE_SENSORS_BIN" 2>/dev/null
 }
 
+# SBC fallback (Raspberry Pi et al.): lm-sensors often reports nothing; SoC
+# temperatures live in /sys/class/thermal/thermal_zone*/{type,temp} (mC).
+read_sysfs_thermal() {
+    [[ -d "$SYSFS_THERMAL_ROOT" ]] || return 1
+    local z type mc found=0
+    for z in "$SYSFS_THERMAL_ROOT"/thermal_zone[0-9]*; do
+        [[ -r "$z/type" && -r "$z/temp" ]] || continue
+        type="$(<"$z/type")" mc="$(<"$z/temp")"
+        [[ "$mc" =~ ^-?[0-9]+$ ]] || continue
+        printf '%s %s\n' "$type" "$mc"
+        found=1
+    done
+    ((found)) || return 1
+}
+
+# Render lm-sensors format block from read_sysfs_thermal lines "type millicelsius".
+format_sysfs_block() {
+    local input="${1:-}" type mc signed n=0
+    [[ -n "$input" ]] || return 1
+    printf 'soc-thermal-virtual-0\nAdapter: Virtual device\n'
+    while read -r type mc; do
+        ((++n))
+        signed="$(awk -v mc="$mc" 'BEGIN { printf "%.1f", mc / 1000 }')"
+        signed="${signed#+}"
+        [[ "$signed" == -* ]] || signed="+$signed"
+        printf 'temp%d:        %s°C\n' "$n" "$signed"
+    done <<<"$input"
+}
+
 main() {
-    local out="" block internal external native
+    local out="" block internal external native="" sysinput
     if native="$(run_native_sensors)" && [[ -n "$native" ]]; then
         out+="$native"$'\n'
+    else
+        native=""
     fi
     if has_temper_probe; then
         if block="$(read_temper 2>/dev/null)" \
@@ -85,8 +117,13 @@ main() {
             echo "warn: TEMPer probe present but read failed" >&2
         fi
     fi
+    if [[ -z "$native" ]] \
+       && sysinput="$(read_sysfs_thermal 2>/dev/null)" \
+       && block="$(format_sysfs_block "$sysinput")"; then
+        out+="$block"$'\n'
+    fi
     [[ -n "$out" ]] || {
-        echo "error: no sensor sources available (lm-sensors pkg? TEMPer venv?)" >&2
+        echo "error: no sensor sources available (lm-sensors pkg? TEMPer venv? sysfs thermal?)" >&2
         return 1
     }
     printf '%s' "$out"