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.

[untitaker]

If we want this feature I think the code is clean. Seems like if the feature won't work the code is still sufficiently isolated from the rest to make this safe to roll out.

[cooperq]

I'm hesitant to merge this for a couple reasons:

1. it adds a lot of code and therefore complexity for a relatively minor feature which could be better solved by notifications and wifi client mode so people don't need cellular plans.
2. It's orbic only meaning we won't have feature parity for other devices.
3. If left on when the device was unplugged this feature could inadvertently cause users to quickly blow through battery life.

Given these hesitations I'm inclined to close this pull request unless a good case is made for merging it.

[PapiJalopy]

Its literally just a toggle that starts a watchdog that monitors 3 sysfs nodes and writes "1" to them if it sees that they have been set to "0". I'm not sure I agree that its complicated.

Me personally I find it useful when paired with my other pull request regarding the severity PNG's. It allows the custom images to always be visible.

[PapiJalopy]

I get the hesitation, but I think this is a little more useful than it may sound on paper.

It is basically just a toggle that starts a small watchdog loop watching a couple sysfs nodes and restoring them if the device turns the display back off. So even though it touches low level stuff, the actual logic is pretty small and self contained.

As for the use case, for me this is mainly about visibility. It is useful with the severity image work, but even outside of that it is helpful any time the device is being used as a dedicated display and the person wants to keep the current state visible without having to constantly wake the screen back up.

On the Orbic only point, I agree it is device specific, but I dont really see that as a blocker by itself. We already have Orbic specific behavior in other places where the hardware exposes capabilities that other devices dont. I wasnt trying to make a cross-device feature here, just expose something the Orbic can already do in a way that is useful.

On battery life, I agree that is the biggest tradeoff, which is why I made it an explicit toggle rather than default behavior. If it helps, I can make that clearer in the UI/config description so people understand that enabling it may increase battery usage if left on while unplugged.