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/nixos/default.nix

@@ -22,7 +22,7 @@ let
   '';
 in
 {
-  imports = [ ./options.nix ./plymouth.nix ./file-manager.nix ./power.nix ./services.nix ./hardware.nix ];
+  imports = [ ./options.nix ./plymouth.nix ./file-manager.nix ./power.nix ./services.nix ./hardware.nix ./timezone.nix ];
 
   config = {
     # The safe half of distro branding: distroName flows into

modules/nixos/options.nix

@@ -46,6 +46,16 @@
     audio.enable = lib.mkEnableOption "the Pipewire audio stack" // { default = true; };
     bluetooth.enable = lib.mkEnableOption "Bluetooth support with blueman" // { default = true; };
 
+    autoTimezone.enable = lib.mkEnableOption ''
+      automatic timezone detection (geoclue + automatic-timezoned): the
+      system timezone — and so the Waybar clock — follows your location, so
+      travelling to another zone updates the time on its own. Off by default
+      (it's a location service and needs the network); toggle it from the
+      System menu, which lands the choice in the in-flake state file. Enabling
+      it unsets the static time.timeZone for you (a runtime timezone needs
+      /etc/localtime writable), so the menu toggle drives a system rebuild''
+      // { default = false; };
+
     snapper.enable = lib.mkEnableOption ''
       hourly/daily BTRFS timeline snapshots of / via snapper, plus the
       `nixos-rebuild-snap` pre-rebuild-snapshot helper. No-op unless the

modules/nixos/timezone.nix

@@ -0,0 +1,87 @@
+# Automatic timezone detection (opt-in) — the system timezone, and so the
+# Waybar clock, follows your location, so travelling to another zone updates
+# the time on its own. Geoclue feeds `automatic-timezoned`, which drives
+# /etc/localtime at runtime.
+#
+# In-flake state, menu-driven (the keyboard/night-light philosophy): the on/off
+# flag lives in the same theme-state.json under `settings.autoTimezone`
+# (git-tracked, reproducible), written by the System-menu toggle
+# (nomarchy-autotimezone). Because this is a SYSTEM service — not a user unit it
+# can start/stop instantly like night-light — the toggle drives a system rebuild
+# (plus a home switch for the Waybar-refresh watcher in timezone.nix home-side).
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.nomarchy.system;
+
+  # Read the same state file the rest of the system side uses (Plymouth too),
+  # wired by lib.mkFlake. The flag defaults off when the file is absent/sparse.
+  state =
+    if cfg.stateFile != null
+    then builtins.fromJSON (builtins.readFile cfg.stateFile)
+    else { };
+  stateEnabled = (state.settings or { }).autoTimezone or false;
+
+  sync = lib.getExe pkgs.nomarchy-theme-sync;
+
+  # Menu/CLI toggle. Runs as the normal user (it owns the flake checkout +
+  # writes the state); sudos only the system switch, like sys-update. Writes
+  # the in-flake flag, then rebuilds: the system rebuild bakes the service +
+  # the time.timeZone override, the home switch installs/removes the Waybar
+  # refresh watcher — both read the same flag we just wrote.
+  nomarchy-autotimezone = pkgs.writeShellScriptBin "nomarchy-autotimezone" ''
+    set -e
+    if [ "$(id -u)" -eq 0 ]; then
+      echo "nomarchy-autotimezone: run as your normal user (it sudos the rebuild itself)" >&2
+      exit 1
+    fi
+    flake="''${NOMARCHY_PATH:-$HOME/.nomarchy}"
+
+    cur=$(${sync} get settings.autoTimezone 2>/dev/null) || cur=false
+    case "''${1:-toggle}" in
+      on)        new=true ;;
+      off)       new=false ;;
+      toggle)    case "$cur" in true|True) new=false ;; *) new=true ;; esac ;;
+      status)    echo "$cur"; exit 0 ;;
+      *) echo "usage: nomarchy-autotimezone [toggle|on|off|status]" >&2; exit 64 ;;
+    esac
+
+    ${sync} --quiet set settings.autoTimezone "$new" --no-switch
+
+    if [ "$new" = true ]; then
+      notify-send "Auto timezone" "Enabling — rebuilding the system…" 2>/dev/null || true
+    else
+      notify-send "Auto timezone" "Disabling — rebuilding the system…" 2>/dev/null || true
+    fi
+
+    sudo nixos-rebuild switch --flake "$flake#default"
+    home-manager switch --flake "$flake"
+
+    if [ "$new" = true ]; then
+      notify-send "Auto timezone on" "The clock now follows your location." 2>/dev/null || true
+    else
+      notify-send "Auto timezone off" "Back to the fixed timezone in system.nix." 2>/dev/null || true
+    fi
+  '';
+in
+{
+  config = lib.mkMerge [
+    {
+      # Shipped unconditionally so the menu can enable the feature even while
+      # it's off. Track the in-flake flag; mkDefault so a hand-set
+      # nomarchy.system.autoTimezone.enable in system.nix still wins.
+      environment.systemPackages = [ nomarchy-autotimezone ];
+      nomarchy.system.autoTimezone.enable = lib.mkDefault stateEnabled;
+    }
+
+    (lib.mkIf cfg.autoTimezone.enable {
+      services.geoclue2.enable = true;
+      services.automatic-timezoned.enable = true;
+      # A runtime timezone needs /etc/localtime writable. automatic-timezoned
+      # sets time.timeZone = null itself, but the installer writes a static
+      # value at normal priority, which would collide (a hard eval error) —
+      # mkForce null overrides both and resolves cleanly.
+      time.timeZone = lib.mkForce null;
+    })
+  ];
+}