add keep_screen_on feature to orbic devices

[PapiJalopy]

Summery

Adds a toggleable keep-screen-on feature that prevents the device display from sleeping. When enabled the daemon detects when the display has entered its sleep state and re-enables it by toggling display sysfs nodes.

Addresses #916 #539

Changes

Adds a toggle in the web UI,

Adds keep_screen_on: bool to config (default is false).

Adds a checkbox and tip to the configuration page.

When keep_screen_on is enabled, spawns a watchdog task that, polls display sysfs state (sleep_mode, bl_gpio, display_on).

If display is blanked (sleep_mode == 0 and bl_gpio == 0), writes 1 to display_on, bl_gpio, andsleep_mode.

No behavior change unless the option is enabled

Documents the new config option in the config.toml.in template and the configuration docs.

Testing

Verified source builds.

Verified binary installs.

Verified toggle is visible in web UI.

With keep_screen_on = true, the screen no longer stays blanked after the normal timeout.

With keep_screen_on = false, behavior matches current upstream behavior.

Pull Request Checklist

• The Rayhunter team has recently expressed interest in reviewing a PR for this.
  • If not, this PR may be closed due our limited resources and need to prioritize how we spend them.
• Added or updated any documentation as needed to support the changes in this PR.
• Code has been linted and run through cargo fmt.
• If any new functionality has been added, unit tests were also added.
• CONTRIBUTING.md has been read.