fix(nightlight): gate hyprsunset on the toggle, drop hardcoded temperature

features/desktop/nightlight.nix previously set
`services.hyprsunset.enable = lib.mkDefault true` unconditionally and
baked the temperature (4000K when toggles.nightlight, 6500K otherwise)
into extraArgs at Nix-eval time. The toggle script bypassed systemd:
pkill on disable, `hyprctl dispatch exec hyprsunset --temperature 4000`
on enable — racing the systemd-managed instance and hardcoding 4000K
regardless of nomarchy.nightlightTemperature. The "Always enabled, we
control via IPC and state" comment was misleading: no IPC, the
temperature was rebuild-time, and the script forked a parallel
process.

Path (b) from the Later row:

  - services.hyprsunset.enable now follows config.nomarchy.toggles.
    nightlight — symmetric with services.hypridle.enable ← toggles.idle.
    Disabled toggle = no process running.
  - extraArgs always reads from config.nomarchy.nightlightTemperature.
    Drops the 6500K neutralising fork; when off the unit just doesn't
    start.
  - nomarchy-toggle-nightlight flips the running systemd user unit via
    `systemctl --user start/stop hyprsunset.service` for instant
    feedback, reads nightlightTemperature from state.json for the
    notify-send line, and writes .nightlight back to state.json so the
    next rebuild realigns services.hyprsunset.enable.

`nix flake check --no-build` + `bash -n` clean.

features/desktop/nightlight.nix

@@ -1,11 +1,21 @@
 { config, lib, ... }:
 
-let
-  temp = toString (if config.nomarchy.toggles.nightlight then config.nomarchy.nightlightTemperature else 6500);
-in
+# hyprsunset (the blue-light filter) is gated on `nomarchy.toggles.nightlight`
+# so a disabled toggle means no process runs — symmetric with how
+# `services.hypridle.enable` is wired off `toggles.idle`. The temperature
+# comes from `nomarchy.nightlightTemperature`, evaluated at Nix-eval time
+# and baked into `extraArgs`. The toggle script (themes/engine/scripts/
+# nomarchy-toggle-nightlight) writes both the toggle and the same
+# temperature value into state.json and flips the systemd unit for
+# instant feedback; the next rebuild's HM activation realigns systemd
+# with the persistent state.
+
 {
   services.hyprsunset = {
-    enable = lib.mkDefault true; # Always enabled, we control via IPC and state
-    extraArgs = lib.mkDefault [ "--temperature" temp ];
+    enable = lib.mkDefault config.nomarchy.toggles.nightlight;
+    extraArgs = lib.mkDefault [
+      "--temperature"
+      (toString config.nomarchy.nightlightTemperature)
+    ];
   };
 }