feat(system): add accessibility preset module

Opt-in `nomarchy.system.accessibility.enable` (default false —
accessibility is a personal preference, not hardware-derived). Wires
`services.gnome.at-spi2-core`, installs `pkgs.orca`, and sets
`XCURSOR_SIZE` to a configurable `accessibility.cursorSize` (default
32, up from NixOS's 24).

The original roadmap entry bundled Hyprland-side bits (slower
key-repeat, Orca launch keybinding, high-contrast palette). Those
require touching home-manager / theme files and a new palette
directory; split into a separate Next-column row so the system-side
preset ships now and the desktop integration follows independently.

docs/ROADMAP.md

@@ -23,7 +23,7 @@ Guardrails (apply when adding anything):
 
 ### Next (bigger lifts that build on Now)
 
-- **Accessibility preset.** Larger cursor, slower key-repeat defaults, `services.orca`, screen reader keybinding, high-contrast theme variant.
+- **Accessibility — home-side companion.** Hyprland-side bits the system preset can't reach: slower `input.repeat_rate` / `repeat_delay` defaults, `SUPER+ALT+S` keybinding to launch Orca, and a high-contrast palette under `themes/palettes/`. Gated on a new `nomarchy.accessibility.enable` mirror of the system option.
 - **Gaming preset.** `programs.steam.enable`, `programs.gamemode.enable`, `services.flatpak.enable` with a curated remote, and a Hyprland window-rule to fullscreen Steam-launched apps.
 - **First-run welcome wizard.** Extend `nomarchy-welcome` from a one-shot greeter into a guided picker: theme, panel position, monospace font, "what's a sane home.nix to start with?". Runs once, persists "done" in `state.json`.
 - **Plymouth theme variants per palette.** Currently one Plymouth theme; could template per-palette so the boot splash matches the active theme.
@@ -124,6 +124,7 @@ Each PR description should reference the row(s) in `docs/SCRIPTS.md` it closes,
 
 (Move items here when they land — keep them brief, link the commit/PR.)
 
+- _2026-04-26_ — Accessibility preset module (`core/system/accessibility.nix`). New `nomarchy.system.accessibility.{enable,cursorSize}` options (opt-in, default off — accessibility isn't a hardware-derived signal). Enables `services.gnome.at-spi2-core`, installs Orca, and sets `XCURSOR_SIZE=32` (configurable). Hyprland-side companion (key-repeat slowdown, Orca keybinding, high-contrast palette) split into a new Next-column row.
 - _2026-04-26_ — Desktop preset module (`core/system/desktop.nix`). New `nomarchy.system.desktop.enable` option; defaults to `formFactor == "desktop"` (mirror of the laptop preset's auto-enable). Pins `powerManagement.cpuFreqGovernor` to `"performance"` and enables `services.zfs.{autoScrub,trim}` so a future ZFS pool gets sensible maintenance for free.
 - _2026-04-26_ — Laptop preset module (`core/system/laptop.nix`). New `nomarchy.system.laptop.{enable,thermald}` options; `enable` defaults to `formFactor == "laptop"` so the installer's existing `formFactor` write auto-flips it on. Wires TLP (governors + 75/80 charge thresholds), force-disables `power-profiles-daemon`, enables `upower` and `thermald` (x86_64), adds the brightnessctl udev rule for backlight without root, and sets a logind lid-switch policy that defers to `hibernation.enable`. Closes both the Now item and the largest Next item.
 - _2026-04-25_ — Software-profile multi-select in the installer. Users can now pick Dev, Gaming, Office, Media, and CLI Utils profiles during install; logic emits corresponding `home.packages` and system toggles into the generated config.