feat: add ambient light sensor (illuminance) support

[CoRfr]

Summary

• Adds support for reading ambient light level (illuminance) from Linux IIO ALS devices via sysfs (/sys/bus/iio/devices/*/in_illuminance_raw)
• Exposes an illuminance sensor (lux) through MQTT with Home Assistant auto-discovery (device_class: illuminance)
• Devices without an ALS gracefully skip the sensor via removeConfig

Implementation

• hardware.js: getIlluminancePath() scans IIO devices for one named als with in_illuminance_raw, getIlluminance() reads the raw lux value, illuminance added to checkSupport()
• integration.js: initIlluminance() / updateIlluminance() following the existing sensor pattern, updated in the 1-minute periodic cycle

Testing

Tested on:

• Surface Pro 3 (HID-SENSOR-200041 via hid-sensor-als driver) — working, reports lux values
• Surface 3 (same driver, dead hardware) — gracefully detects ALS support but sensor returns 0; removeConfig would apply on devices with no IIO ALS at all

Notes

The IIO ambient light sensor is commonly available on tablets and laptops with HID sensor hubs (Surface devices, ThinkPads, etc.). The sensor name als is the standard name used by the hid-sensor-als kernel driver.

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