Trigger the pre-close warning

POST http://{deviceHost}/button/Pre-close%20Warning/press

Manually triggers the pre-close warning sequence (audible beeps and LED flash). The
firmware automatically executes this before every close command — you do not need to call
this endpoint before calling /cover/Garage%20Door/close. Use it only if you want to
trigger the warning independently.

v2 → v3: /button/pre_close_warning/press → /button/Pre-close%20Warning/press