feat(system): make night light settings-driven

[mateoalfaro]

Reworks NightLightManager from a hard-coded 4000 K on/off toggle into a passive, settings-driven state machine backed by the dev.sinty.desktop schema.

• Adds a master switch, configurable temperature clamped to 1000–6500 K, and an optional adaptive schedule using HH:MM start/end times.

• Effective state is:

  enabled && (!adaptive || is_night())
  

  enabled now reflects the effective state rather than the raw switch.

• Every settings change triggers refresh(), which:

  • Re-applies the backend only when the state or temperature actually changes.
  • Emits changed() on effective-state changes.
  • Re-arms a Timeout for the next schedule boundary.
  • Handles overnight spans.
  • Treats from == to as never night.

• toggle() and the new setters only write settings; propagation happens through the settings.changed signal.

The GammaBackend interface and singleton are unchanged, and no other code calls the removed enable() / disable() methods.

Tested on

• NixOS
• Fedora 44

[perlowja]

Heads up — this rework reads five GSettings keys that do not exist in the schema, which hard-crashes the shell (SIGABRT) the first time the sidebar is opened.

`NightLightManager` now reads `night-light-enabled`, `night-light-adaptive`, `night-light-temperature`, `night-light-adaptive-from` and `night-light-adaptive-to`, but none of them are defined in dev.sinty.desktop.gschema.xml (which lives in the singularity-desktop supertree, data/). GSettings aborts the process on an unknown key, so SystemMonitor.get_night_light() kills the shell as soon as Sidebar is lazily constructed — i.e. on the first click on the panel.

Measured on a CIX Sky1 board (Radxa Orion O6N) 2026-08-17, via systemd-coredump:

#16 singularity_system_monitor_get_night_light
#17 singularity_system_view_construct
#18 singularity_sidebar_construct
...  g_signal_emit ...
#61 main
Process ... terminated abnormally with signal 6/ABRT

It then crash-loops, because the supervisor restarts the shell and the next sidebar construction aborts again.

I hit this because I merged this branch locally to unblock an unrelated build (singularity-shell main already calls set_schedule_from/set_temperature/TEMP_MIN/TEMP_MAX, so the shell does not build without this PR). Fixed on our side by adding the five keys to the schema — singularityos-lab/singularity-desktop 2e862db — with defaults matching the previous hard-coded behaviour (off, 4000 K), so it is behaviour-preserving. Happy to open that as a PR against singularity-desktop if you would rather it land alongside this one.

Same failure class as the window-border-width / tiling-spacing keys already called out in that schema file, if you want prior art for the fix shape.

[mateoalfaro]

Hey, I am confused about this report as the schema additions have been merged upstream into singularityos-lab/singularity-desktop@4a69ba2 did your local build have the latest version of that repo?