docs(roadmap): note night-light toggle is session-scoped; persistent-off follow-up

The menu/Waybar toggle stops hyprsunset for the session only — it's
WantedBy=graphical-session.target, so the next login auto-starts it and the
off-state doesn't persist (deliberate "true colours for now" behaviour).
Record the persistent-off option (a state marker honoured via the unit's
ConditionPathExists) as an optional follow-up so it isn't forgotten.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -387,9 +387,15 @@ how to override it. Items marked ✓ are shipped.
   `nomarchy-menu nightlight` entry (System submenu, self-gated on the unit
   existing) and a self-gating Waybar `custom/nightlight` indicator (moon = on,
   sun = off; in the generated bar and both summer whole-swaps) drive it.
-  Remaining (optional): geo (lat/long) auto sunset/sunrise (would mean
-  wlsunset, which schedules by location). Pending an on-machine check that
-  stopping hyprsunset cleanly restores the gamma.
+  The toggle is **session-scoped by design**: `stop` halts the running unit
+  but it's `WantedBy=graphical-session.target`, so the next login auto-starts
+  it and night-light returns to its schedule (off never persists). Remaining
+  (optional): (1) **persistent off** — a state marker
+  (`~/.local/state/nomarchy/nightlight-off`) the unit honours via
+  `ConditionPathExists=!%h/…`, so a manual off survives logout/reboot until
+  toggled back; (2) geo (lat/long) auto sunset/sunrise (would mean wlsunset,
+  which schedules by location). Pending an on-machine check that stopping
+  hyprsunset cleanly restores the gamma.
 - **Keyboard layouts (per-device + switching):**
   - ✓ **Per-device declarative layout:** `nomarchy.keyboard.devices`
     (`{ "<hyprctl-device-name>" = { layout; variant; }; }`) generates Hyprland