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>

modules/home/rofi.nix

@@ -324,6 +324,14 @@ ${themeRows}
           && exec nomarchy-nightlight toggle
         notify-send "Night light" "Not available (nomarchy.nightlight off?)."; exit 0 ;;
 
+      autotimezone)
+        # Toggle automatic timezone detection (geoclue + automatic-timezoned).
+        # A SYSTEM service, so flipping it writes the in-flake flag and runs a
+        # system rebuild (sudo) + a home switch — in a terminal, like Snapshots.
+        command -v nomarchy-autotimezone >/dev/null 2>&1 \
+          || { notify-send "Auto timezone" "Unavailable on this machine."; exit 0; }
+        exec ${cfg.terminal} -e nomarchy-autotimezone toggle ;;
+
       snapshot)
         # btrfs-assistant 2.2 segfaults on 26.05 (libbtrfsutil ABI), so launch
         # the keyboard-driven snapper browser instead: a terminal running it
@@ -374,6 +382,10 @@ ${themeRows}
           then row "Night light (on)"  weather-clear-night
           else row "Night light (off)" weather-clear-night
           fi
+          if [ "$(nomarchy-theme-sync get settings.autoTimezone 2>/dev/null)" = true ]
+          then row "Auto timezone (on)"  preferences-system-time
+          else row "Auto timezone (off)" preferences-system-time
+          fi
           command -v nomarchy-snapshots >/dev/null 2>&1 && row "Snapshots" timeshift
           if [ -e "''${bats[0]}" ] && command -v powerprofilesctl >/dev/null 2>&1; then
             row "Power profile" preferences-system-power
@@ -388,6 +400,7 @@ ${themeRows}
           *Printers*)         exec "$0" printers ;;
           *"Do Not Disturb"*) exec "$0" dnd ;;
           *"Night light"*)    exec "$0" nightlight ;;
+          *"Auto timezone"*)  exec "$0" autotimezone ;;
           *Snapshots*)        exec "$0" snapshot ;;
           *"Power profile"*)  exec "$0" power-profile ;;
         esac ;;
@@ -414,7 +427,7 @@ ${themeRows}
         esac ;;
 
       *)
-        echo "usage: nomarchy-menu [tools|system|power|power-profile|theme|clipboard|calc|files|emoji|web|network|bluetooth|audio|printers|capture|keybinds|ask|dnd|nightlight|snapshot]" >&2
+        echo "usage: nomarchy-menu [tools|system|power|power-profile|theme|clipboard|calc|files|emoji|web|network|bluetooth|audio|printers|capture|keybinds|ask|dnd|nightlight|autotimezone|snapshot]" >&2
         exit 64 ;;
     esac
   '';