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>

agent/BACKLOG.md

@@ -64,7 +64,6 @@ HARDWARE-QUEUE. Close #76 on PASS.
 - **Installer round 2** (ROADMAP § Installer): multi-disk BTRFS RAID,
   impermanence, BIOS/legacy boot.
 - **Boot-from-snapshot**: a systemd-boot equivalent of grub-btrfs.
-- **Night-light geo mode**: lat/long auto sunset/sunrise (means wlsunset).
 - **MIPI/IPU software-ISP camera** support (no-UVC machines).
 - **VPN exit-node richer display** (country/city) (optional).
 - **NixOS release bump → v2** `[human]`: deliberate, hand-edited, never