feat(idle): unlock by fingerprint, and say so — hyprlock never used the PAM flag

Bernardo tested the lock screen after turning `fingerprint.pam` on: sudo took
a finger, hyprlock did nothing. The PAM stack was not the problem — grosshack
sits in /etc/pam.d/hyprlock at order 11400 exactly like sudo's. hyprlock just
never asks it: its PAM conversation runs only on submit, so a module that
wants to prompt *while* polling the reader never gets a turn. hyprlock has its
own fprintd-over-D-Bus backend instead, behind `auth:fingerprint:enabled`,
which nothing in the distro ever set. So `fingerprint.pam = true` promised
"login + sudo" and silently skipped the surface you meet most often.

The second half is the one worth having: enabling the backend alone yields a
reader that works while the field still reads "password…". $FPRINTPROMPT is
the ONLY slot hyprlock renders the ready/scanning/failed messages into, and
ours hardcoded the placeholder — proven on hardware, where a test config with
the backend on unlocked by finger and said nothing whatsoever. A feature that
works and cannot be discovered fails VISION's "discoverable without reading
the README" either way, so the placeholder now carries $FPRINTPROMPT and the
messages mirror sudo's "Enter Password or Place finger".

New `nomarchy.idle.fingerprint` (default false), mirroring
`nomarchy.hardware.fingerprint.pam` the way `nomarchy.keyboard.layout` mirrors
`services.xserver.xkb.layout`: hyprlock is configured in standalone Home
Manager, which has no `osConfig` to derive the NixOS side from. Opt-in rather
than implied, because with no reader hyprlock advertises a scan that cannot
happen. Documented in the template (SoT for opt-in comments) and README —
option-docs caught the missing row, which is the check doing its job.

Verified V2: nix flake check --no-build; checks.option-docs passes (failed
first with "undocumented option", as it should). V3 pending: Bernardo applies
it and confirms the field reads "password… or scan finger" and both factors
work — the mechanism itself is already proven on his reader via a test config.

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

README.md

@@ -248,6 +248,7 @@ two tables below are split along exactly that line.
 | `nomarchy.dockAudio.enable` | `true` | On a fresh external-monitor plug, PipeWire/WirePlumber are reprobed after hardware settles and the highest-priority available HDMI/DP/USB sink becomes default, with a toast and journal result. A later manual speaker choice sticks until the next physical plug; unplug falls back to built-in. Manual route: System › Audio |
 | `nomarchy.firstBootWelcome.enable` | `true` | One dismissible “you're set” toast on the first session (SUPER+M / SUPER+T / SUPER+? + network pointer); marker is `settings.firstBootShown` in the flake checkout |
 | `nomarchy.idle.enable` | `true` | hyprlock + hypridle (idle lock 5 min, display off 10, suspend 15 min — battery-only) |
+| `nomarchy.idle.fingerprint` | `false` | Unlock the lock screen with a fingerprint as well as the password, and say so on the input field. Set it alongside `nomarchy.hardware.fingerprint.pam` in system.nix: hyprlock is configured from Home Manager, which cannot read the NixOS option — and hyprlock does **not** take a fingerprint through PAM at all (its PAM stack runs only on submit), so it uses its own fprintd backend that this switch turns on |
 | `nomarchy.yazi.enable` | `true` | yazi TUI file manager, themed + curated plugins |
 | `nomarchy.osd.enable` | `true` | swayosd on-screen display for volume/brightness/mute |
 | `nomarchy.shell.enable` | `true` | zsh + starship prompt + bat/eza/zoxide (zsh is the default login shell) |