Heltec V3 screen/LED controls and display

[Koreanman01]

Summary

• Heltec V3‑only screen/LED controls with persistence, UI, and CLI actions.
• Heltec V3‑specific SSD1306 display driver with brightness control.
• Heltec V3 overlay examples to avoid shared example edits.
• VEXT polarity fix for correct brightness.
• Persistence uses ESP32 NVS (no Preferences dependency).

Details

• Adds board settings for screen/LED/brightness and applies them at runtime.
• LED/brightness persist across reboots; screen defaults to on by design.
• Introduces a Heltec V3 display class (contrast/precharge/VCOM handling).
• Updates Heltec V3 build flags and overlay example selection.

Testing

• Built and uploaded Heltec_v3_companion_radio_usb
• Built and uploaded Heltec_v3_companion_radio_ble
• Built and uploaded Heltec_v3_repeater

[oltaco]

Thanks for this, brightness control will be a great addition. In future please base all PRs against dev branch, PRs against main branch will not be accepted.

I really think this should be implemented in the main SSD1306 display driver so that all devices with SSD1306 can benefit rather than copying the firmwares into the heltec v3 variant folder and adding the feature there.

It's also probably not appropriate to use EnvironmentSensorManager's getNumSettings(), getSettingName(), getSettingValue(), and setSettingValue() methods for setting the display brightness, I think it would require new CMD_GET/SET and PUSH_ codes for companion firmwares and could be integrated with settings in the on device UI.