feat(greeter): tuigreet + console themed from the state JSON (item 16)

New modules/nixos/greeter.nix owns the greetd block (moved out of
default.nix) plus the theming, the Plymouth model — baked at SYSTEM
rebuild from nomarchy.system.stateFile. Two parts, because tuigreet
draws on the VT with the 16 ANSI slots: console.colors becomes the
theme's ansi[] (vt.default_* kernel params — which also themes raw
ttys and the LUKS passphrase prompt), and tuigreet gets a --theme of
NAMED slots (its parser is ratatui Color::from_str, checked in source;
the names map to the standard indexes the retinted palette now
serves). A sparse state without ansi skips theming cleanly.

Verified: V0; V1 — the template-system toplevel bakes the full --theme
spec into greetd.toml and all three vt.default_{red,grn,blu} palettes
into kernel-params. A checks.greeter VM test was attempted and dropped
after bisecting: tuigreet dies under runNixOSTest even without the
flag (harness limit; nixpkgs's own greetd test uses agreety) —
recorded in agent/MEMORY.md. Remains: V3 rendering +
theme-follows-rebuild on hardware (HARDWARE-QUEUE).

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

agent/HARDWARE-QUEUE.md

@@ -153,6 +153,13 @@ QA machine), the **T14s** (webcam case).
       applies the matching profile within ~3s (toast names it);
       unplugging switches back; Auto-switch off stops that; with two
       profiles naming the same outputs, no flapping (ties do nothing).
+- [ ] **Themed greeter + console (item 16)** — after `sys-rebuild` +
+      logout: tuigreet renders in theme colors (dark container, accent
+      border, themed prompt/time) and a raw tty (CTRL+ALT+F2) shows the
+      theme's ANSI palette; on a LUKS machine the passphrase prompt
+      follows too. Then switch theme + `sys-rebuild` + logout → the
+      greeter follows the new palette. (tuigreet can't run under the
+      VM harness — see MEMORY.md — so rendering is hardware-tier.)
 - [ ] **Color picker (item 13, final slice)** — SUPER+CTRL+P (or Tools ›
       Color picker): hyprpicker's zoom loupe appears; click a pixel →
       toast shows the hex and `wl-paste` yields it; Esc cancels with no