feat(timezone): opt-in automatic, location-following timezone

nomarchy.system.autoTimezone (off by default): geoclue + automatic-
timezoned drive /etc/localtime from your location, so travelling to
another zone updates the Waybar clock on its own.

Menu-driven, in-flake state (the night-light / keyboard philosophy):
the flag is settings.autoTimezone in theme-state.json (git-tracked); a
System-menu entry toggles it. Because it's a SYSTEM service — not a user
unit it can start/stop instantly like night-light — the toggle
(nomarchy-autotimezone, run in a terminal) writes the flag --no-switch
then drives `sudo nixos-rebuild` (bakes the service + the time.timeZone
override) plus `home-manager switch` (the Waybar-refresh watcher); both
sides read the one flag.

- modules/nixos/timezone.nix: parses settings.autoTimezone from
  nomarchy.system.stateFile (like Plymouth), gates geoclue2 +
  automatic-timezoned, and mkForce-nulls time.timeZone — automatic-
  timezoned sets it null at normal priority, which collides with the
  installer's static value (a hard eval error), so force wins and
  reverts cleanly when disabled. Ships the nomarchy-autotimezone toggle.
- modules/home/timezone.nix: a tiny user service watching timedate1's
  change signal that reloads Waybar (SIGUSR2) on a real zone change, so
  the clock follows live (Waybar captures the zone at construction).
  Gated on the same flag via nomarchy.settings.autoTimezone.
- rofi menu: "Auto timezone (on/off)" in the System submenu.
- option + template example + ROADMAP entry; theme.nix seeds the flag.

Eval-verified on (geoclue+daemon on, tz forced null over a static
installer value, watcher present) and off (static tz intact, nothing
extra); home + system both build green. Needs an on-hardware check
(geoclue detection + the SIGUSR2 clock refresh aren't CI-testable).

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

docs/ROADMAP.md

@@ -492,6 +492,30 @@ how to override it. Items marked ✓ are shipped.
   sunset/sunrise (would mean wlsunset, which schedules by location). Pending an
   on-machine check (first enable rebuilds + comes on; later toggles instant; off
   persists across reboot via ExecCondition; stopping hyprsunset restores gamma).
+- ✓ **Automatic timezone (location-following clock):** `nomarchy.system.autoTimezone`
+  (opt-in, off by default) — geoclue + `services.automatic-timezoned` drive
+  `/etc/localtime` from your location, so travelling to another zone updates the
+  Waybar clock on its own. **Menu-driven, in-flake state** (the night-light /
+  keyboard philosophy): the flag is `settings.autoTimezone` in theme-state.json,
+  git-tracked; the System-menu entry (`nomarchy-menu autotimezone` →
+  `nomarchy-autotimezone`) writes it and rebuilds. **Not instant like
+  night-light** — it's a *system* service (not a user unit you can start/stop),
+  so the toggle drives a `sudo nixos-rebuild` (bakes the service + the
+  `time.timeZone` override) plus a `home-manager switch` (the Waybar-refresh
+  watcher), both off the one flag. **time.timeZone handling:** a runtime zone
+  needs `/etc/localtime` writable; automatic-timezoned sets `time.timeZone = null`
+  itself, but the installer's static value would collide (a hard eval error), so
+  the module forces it null (`mkForce`) over the installer's value when enabled,
+  and reverts to it when disabled. **Live clock refresh:** Waybar's clock module
+  captures the zone at construction, so `modules/home/timezone.nix` runs a tiny
+  user service that watches timedate1's change signal and reloads Waybar
+  (SIGUSR2) on a real zone change (also catches a manual `timedatectl
+  set-timezone`). Eval-verified both ways (on: geoclue+daemon on, tz forced null
+  over a static installer value, watcher present; off: static tz intact, no
+  service/watcher). **Pending an on-hardware check** — geoclue detection and the
+  SIGUSR2 clock refresh aren't testable in CI (if SIGUSR2 proves insufficient,
+  fall back to restarting waybar). Remaining (optional): a Waybar tooltip line
+  showing the detected zone.
 - **Keyboard layouts (per-device + switching):**
   - ✓ **Per-device declarative layout:** `nomarchy.keyboard.devices`
     (`{ "<hyprctl-device-name>" = { layout; variant; }; }`) generates Hyprland