feat(fingerprint): password OR fingerprint in parallel at one prompt

Bernardo promoted the PROPOSED item live: with fingerprint PAM on,
sudo/login should accept whichever factor comes first instead of
pam_fprintd's wait-for-the-reader-then-password. Stock PAM cannot
express parallel factors (linux-pam#301), so this packages
pam-fprint-grosshack v0.3.0 (pkgs/, pinned from GitLab — the
field-standard fprintd fork), source-reviewed before packaging: every
failure path (no reader, no prints, fprintd absent/hung, timeout,
password typed) returns PAM_AUTHINFO_UNAVAIL and falls through; a
typed password is only ferried via PAM_AUTHTOK to the stock
`auth sufficient pam_unix.so … try_first_pass` rule — the module never
validates passwords itself, so it cannot lock out password login.

New option nomarchy.hardware.fingerprint.parallel, default TRUE (the
better UX is what opting into fingerprint PAM buys; false = stock
sequential). Wiring swaps the modulePath of stock fprintd's rule slot
(mkForce) so the sufficient-before-pam_unix ordering is inherited, not
recomputed. README + downstream template rows added.

Verified: V2 — checks.hardware-toggles extended to three nodes, green:
parallel node asserts the grosshack auth line precedes pam_unix in
/etc/pam.d/sudo and that with NO reader a correct password still
passes sudo while a wrong one fails (the lockout-safety invariant);
seqpam node gets stock pam_fprintd and no grosshack; nopam gets
neither. flake check + option-docs + template-sot green.
V3 pending (HARDWARE-QUEUE, AMD dev box): the real type-or-touch race,
fprintd-stopped fallback, hyprlock/greeter after a fingerprint win.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

templates/downstream/system.nix

@@ -63,6 +63,7 @@
   #   amd.rocm.gfxOverride = "11.0.0";          #   HSA override for an unlisted iGPU
   #   fingerprint.enable = true;                #   fprintd; installer-set when a reader is detected
   #   fingerprint.pam = true;                   #   use the fingerprint for login + sudo
+  #   fingerprint.parallel = false;             #   sequential prompt instead of password-or-finger
   #   npu.enable = true;                        #   on-die NPU driver (experimental; userspace runtime BYO)
   #   latestKernel = true;                       #   newest kernel for very-new hardware (drivers not yet in the default)
   #   camera.hideIrSensor = true;               #   dual-sensor webcam: hide the IR node so apps get the color cam