Keep overheat warning active during self protect

[0xjc65eth]

Summary

• update the in-memory overheat state immediately when self protect mode starts
• clear the in-memory overheat state only after recovery successfully restarts mining

Why

The dashboard and display read the in-memory SYSTEM_MODULE.overheat_mode value. During self protect recovery, the firmware persisted the NVS flag immediately but did not update the runtime state until later in the power-management loop, so the warning could disappear while the device was still cooling/recovering.

Fixes #1638.

Testing

• git diff --check

Full firmware build was not run locally because idf.py is not installed in this shell and the Docker daemon is not running.

[0xjc65eth]

Closing this for now to reduce maintainer review load, per feedback from @mutatrum. I am keeping #1705 open as the single focused PR because it is small, UI-only, and already has an ack. Happy to revisit this later only if maintainers ask for it. Thanks for the feedback and for maintaining the project.