feat(nightlight): geo mode — lat/long-computed sunset via wlsunset

Set BOTH nomarchy.nightlight.latitude/.longitude and the night light
switches backing unit: wlsunset computes sunrise/sunset from the
location daily (the fixed .sunrise/.sunset are ignored;
.temperature feeds the night temp). Everything user-facing is
unchanged — same nomarchy-nightlight toggle script, Waybar moon, and
live-state ExecCondition gate; the unit name is a single let-binding
so all three follow together. Declarative-only on purpose: coordinates
are machine config like the keyboard layout, so home.nix (commented
template example), not a menu writer.

checks.nightlight-geo guards the wiring at pure eval: rendered
wlsunset ExecStart carries the coords + night temperature, the
ExecCondition gate landed on the swapped unit, hyprsunset stays off in
geo mode.

Verification: V1 — nix flake check --no-build exit 0 (evals the new
asserts + option-docs sync); built downstream-template-home (default
hyprsunset path unregressed). V3 pending: visible warm shift at the
location's night + instant toggle/off-persistence on the swapped unit
(HARDWARE-QUEUE § Any machine).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

templates/downstream/home.nix

@@ -32,6 +32,9 @@
   #   temperature = 4000;               #   night warmth in K — lower is warmer
   #   sunset = "20:00";
   #   sunrise = "07:00";
+  #   latitude = "52.52";               #   geo mode: set BOTH lat/long and sunrise/
+  #   longitude = "13.40";              #   sunset follow your location (wlsunset);
+  #                                     #   the fixed times above are then ignored
   # };
   #
   # nomarchy.updates = {                # passive update-awareness indicator + notification