feat(menu): one fingerprint switch, an auto-login toggle, and the state bridge they needed

Bernardo, post-reboot: "Use for login" was the wrong question. Whether the
finger works is one decision, not two, and whether login prompts at all is
a different decision that was never in the menu.

System › Fingerprint is now a single Fingerprint (on/off) switch, leading
the menu with enroll/list/verify/delete as the plumbing behind it. It
writes the one settings.fingerprint.pam key, and modules/home/idle.nix now
defaults idle.fingerprint from that same key — so the lock screen and
login/sudo move together instead of drifting apart the way they did until
e2de906. nomarchy-fingerprint does the two rebuilds this needs (sudo
system for PAM, home switch for hyprlock) and refuses to turn on with no
finger enrolled.

System › Auto-login is new (nomarchy-autologin), and it is what decides
whether anything is asked at boot: auto-login on means no prompt whatever
the fingerprint switch says; off means the greeter asks, for a password or
a finger. Installer-seeded ON for LUKS machines — the passphrase already
gates the disk — and off without it, where the greeter is the only thing
between power-on and the desktop.

Both had to become state-owned to be toggleable at all, which surfaced two
real bugs:

  * nomarchy.system.greeter.autoLogin defaulted from
    `config.nomarchy.settings…` — an attribute that exists ONLY on the Home
    Manager side. On NixOS it is absent and `or null` swallowed the error,
    so the default silently evaluated to null on every machine ever built.
    That is why the installer baked a Nix line: the state path never
    worked. Now read via theme-state-read.nix (the hardware.nix/timezone.nix
    pattern) and mkDefault'd, so the menu owns it and a hand-set line still
    pins it. Two more options read the same phantom bridge — BACKLOG #116.
  * `theme-sync get` printed Python's "None" for a JSON null, so every
    `case … null)` a caller writes would miss. Now prints "null", as the
    comment above it already promised for booleans.

The installer seeds the state instead of emitting the system.nix line,
because that line outranks the state and would strand the toggle.

V1 (V3 pending: HARDWARE-QUEUE). nix flake check --no-build, installer-
safety and option-docs all pass. Proved by eval/build, not assumed: a state
carrying autoLogin yields greetd initial_session {"user":"bernardo"}, the
template state (no autoLogin) yields none, and a hand-set null beats a state
that says otherwise; a state with only fingerprint.pam=true — nothing set by
hand — renders the hyprlock auth.fingerprint block; both new tools pass
bash -n and land in systemPackages (nomarchy-fingerprint only with a
reader); the patcher writes settings.greeter.autoLogin and no system.nix
line; and the get round trip prints null, so the menu reads "Auto-login
(off)" where it would have read "(on)".

The reader itself, the two rebuilds, and the reboot are hardware — queued.

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

modules/home/options.nix

@@ -367,23 +367,29 @@ in
     dockAudio.enable = lib.mkEnableOption "settled PipeWire/WirePlumber reprobe and automatic default-output switch to an available dock/monitor sink (HDMI/DisplayPort/USB) on fresh display hotplug, with a toast and journal result; a later manual choice sticks until the next plug" // { default = true; };
     firstBootWelcome.enable = lib.mkEnableOption "one dismissible \"you're set\" toast on the first session (menu/themes/keys + network pointer); marker is settings.firstBootShown in the flake checkout" // { default = true; };
     idle.enable = lib.mkEnableOption "hyprlock + hypridle (idle lock, display off, suspend)" // { default = true; };
-    idle.fingerprint = lib.mkEnableOption ''
-      unlocking the lock screen with a fingerprint as well as the password,
-      and saying so on the input field.
+    idle.fingerprint = lib.mkOption {
+      type = lib.types.bool;
+      default = config.nomarchy.settings.fingerprint.pam or false;
+      defaultText = lib.literalExpression
+        "(settings.fingerprint.pam from theme-state.json) or false";
+      description = ''
+        Unlock the lock screen with a fingerprint as well as the password, and
+        say so on the input field.
 
-      Mirrors `nomarchy.hardware.fingerprint.pam` in system.nix — keep the two
-      matched, the same way `nomarchy.keyboard.layout` matches
-      `services.xserver.xkb.layout`. It cannot be derived: hyprlock is
-      configured here, in standalone Home Manager, which has no `osConfig` to
-      read the NixOS side from.
+        Reads the SAME `settings.fingerprint.pam` state key that
+        `nomarchy.hardware.fingerprint.pam` defaults from, so the one
+        System › Fingerprint toggle moves the lock screen and login/sudo
+        together — "fingerprint on" is one decision, not two that can drift.
+        (It has to arrive by state, not by reading the NixOS side: hyprlock is
+        configured here, in standalone Home Manager, which has no `osConfig`.)
 
-      Deliberately separate from the PAM flag rather than implied by it:
-      hyprlock does NOT unlock by fingerprint through PAM. Its PAM stack only
-      runs on submit, so a parallel module never gets to poll — hyprlock has
-      its own fprintd-over-D-Bus backend instead, and this is the switch for
-      it. With no reader present it advertises a scan that cannot happen, so
-      it stays opt-in
-    '';
+        The two remain separate *mechanisms*, which is why this option still
+        exists to be set by hand: hyprlock does NOT unlock by fingerprint
+        through PAM. Its PAM stack only runs on submit, so a parallel module
+        never gets to poll — hyprlock has its own fprintd-over-D-Bus backend
+        instead, and this is the switch for it.
+      '';
+    };
     yazi.enable = lib.mkEnableOption "the yazi TUI file manager, themed with a curated plugin set" // { default = true; };
     osd.enable = lib.mkEnableOption "swayosd on-screen display for volume/brightness/mute" // { default = true; };
     shell.enable = lib.mkEnableOption "the zsh shell experience (starship prompt, bat/eza/zoxide)" // { default = true; };