Add SmartThings Edge driver and SMARTTHINGS.md setup guide

[ifnull]

Summary

Adds a Samsung SmartThings path for AirCube on Zigbee hubs that support Edge: Lua driver under smartthings/aircube-zigbee/, user guide SMARTTHINGS.md (pairing, CLI package/channel/install, Advanced Web App check), and smartthings/driver-channel.json for edge:channels:create with StuckAtPrototype Terms of Service URL.

Updates README and CONTRIBUTING (SmartThings section, project layout, Zigbee note).

Why

Out of the box the hub often matches AirCube as a generic humidity/temperature device. Custom cluster 0xFC01 (eCO2, eTVOC, AQI) needs an explicit Edge driver; behavior is aligned with existing ZHA / Z2M integration in this repo.

How to verify

1. Pair AirCube, confirm temp/humidity in the app.
2. From repo root: smartthings edge:drivers:package . in smartthings/aircube-zigbee/, assign to a channel, enroll hub, install driver, switch driver or re-pair.
3. Confirm AirCube Zigbee driver and all five readings in the app / Advanced Web App.

Notes

• LED brightness (Analog Output 0x000D) is not in this driver v1.
• Apache-2.0 consistent with the rest of the project.