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/timezone.nix

@@ -0,0 +1,44 @@
+# Auto-timezone, home side: keep the Waybar clock in step with the system
+# timezone. Waybar's clock module captures the zone once at construction, so a
+# runtime timezone change (automatic-timezoned, nomarchy.system.autoTimezone)
+# would NOT show until a relogin. A tiny watcher subscribes to timedate1's
+# change signal and reloads Waybar (SIGUSR2 = the same reload theme-sync uses),
+# so the clock follows your location live. Also catches a manual
+# `timedatectl set-timezone`.
+#
+# Gated on the same in-flake flag the system side reads (settings.autoTimezone,
+# exposed via nomarchy.settings) — so it only runs when the feature is on. The
+# menu toggle (nomarchy-autotimezone) rebuilds both sides off that one flag.
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.nomarchy;
+  enabled = cfg.waybar.enable && (cfg.settings.autoTimezone or false);
+
+  tzWatch = pkgs.writeShellScript "nomarchy-tz-watch" ''
+    last=$(${pkgs.systemd}/bin/timedatectl show -p Timezone --value 2>/dev/null || true)
+    ${pkgs.dbus}/bin/dbus-monitor --system \
+      "type='signal',interface='org.freedesktop.DBus.Properties',path='/org/freedesktop/timedate1',member='PropertiesChanged'" \
+      2>/dev/null |
+    while read -r _; do
+      cur=$(${pkgs.systemd}/bin/timedatectl show -p Timezone --value 2>/dev/null || true)
+      [ "$cur" = "$last" ] && continue
+      last=$cur
+      ${pkgs.procps}/bin/pkill -SIGUSR2 -x waybar 2>/dev/null || true
+    done
+  '';
+in
+{
+  systemd.user.services.nomarchy-tz-watch = lib.mkIf enabled {
+    Unit = {
+      Description = "Reload Waybar on timezone change (auto-timezone)";
+      PartOf = [ "graphical-session.target" ];
+      After = [ "graphical-session.target" ];
+    };
+    Service = {
+      ExecStart = "${tzWatch}";
+      Restart = "on-failure";
+    };
+    Install.WantedBy = [ "graphical-session.target" ];
+  };
+}