fix: centralize state defaults via lib/state-schema.nix

Kills a recurring bug class: state defaults previously lived in three
parallel places that drifted apart over time.

  - lib/state-schema.nix          (the canonical schema, referenced
                                   nowhere except a description string)
  - core/system/options.nix       (default = "..." clauses on options)
  - core/home/options.nix         (same, on home options)
  - core/home/state.nix           (`or "..."` fallbacks for state.json reads)

When `state.json` is missing a key, three files have to agree on the
fallback. They keep silently drifting:

  - The OOTB QA audit shipped fixes for this pattern.
  - Earlier this session, `chore: switch default theme summer-night → nord`
    fixed core/system/options.nix and core/home/state.nix — but missed
    core/home/options.nix, which still defaulted nomarchy.theme to
    "summer-night". Every consumer of the home option
    (features/default.nix, vscode.nix, waybar, hyprland, theme engine)
    resolved to the wrong theme when state.json was blank.

This change:

  - Imports lib/state-schema.nix into all three consumers and replaces
    every hardcoded default with `schema.<scope>.<key>`.
  - Fixes the lingering nomarchy.theme = "summer-night" home-side bug as
    a side-effect.
  - Touches roughly 25 literals across the three files.

Verified `nix flake check --no-build` passes and every centralized value
evaluates to the exact literal it previously had. Off-schema option-only
defaults (isLightMode, formFactor, cursor.*, iconsTheme, keyring.enable,
etc.) are left hardcoded — they have no state.json counterpart, so
there's no source-of-truth split to resolve.

Out of scope (follow-up):
  - Have installer/install.sh generate /mnt/etc/nixos/state.json from
    the schema instead of hardcoded JSON — would close the last
    split-brain surface (the installer can still drift from schema).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/home/options.nix

@@ -1,47 +1,52 @@
 { lib, pkgs, ... }:
 
+let
+  # Defaults live in lib/state-schema.nix so they can't drift between this
+  # file, core/system/options.nix, and core/home/state.nix's `or` fallbacks.
+  schema = import ../../lib/state-schema.nix { inherit lib; };
+in
 {
   options.nomarchy = {
     toggles = {
       suspend = lib.mkOption {
         type = lib.types.bool;
-        default = true;
+        default = schema.home.suspend;
         description = "Whether to show suspend in system menu.";
       };
       screensaver = lib.mkOption {
         type = lib.types.bool;
-        default = true;
+        default = schema.home.screensaver;
         description = "Whether the screensaver is enabled.";
       };
       idle = lib.mkOption {
         type = lib.types.bool;
-        default = true;
+        default = schema.home.idle;
         description = "Whether the idle lock is enabled.";
       };
       nightlight = lib.mkOption {
         type = lib.types.bool;
-        default = false;
+        default = schema.home.nightlight;
         description = "Whether the nightlight is enabled.";
       };
       waybar = lib.mkOption {
         type = lib.types.bool;
-        default = true;
+        default = schema.home.waybar;
         description = "Whether the top bar is enabled.";
       };
       skipVsCodeTheme = lib.mkOption {
         type = lib.types.bool;
-        default = false;
+        default = schema.home.skipVsCodeTheme;
         description = "Whether to skip theme changes in VSCode.";
       };
     };
     nightlightTemperature = lib.mkOption {
       type = lib.types.int;
-      default = 4000;
+      default = schema.home.nightlightTemperature;
       description = "Temperature for the nightlight.";
     };
     theme = lib.mkOption {
       type = lib.types.str;
-      default = "summer-night";
+      default = schema.home.theme;
       description = "System theme name.";
     };
     formFactor = lib.mkOption {
@@ -58,35 +63,35 @@
     };
     wallpaper = lib.mkOption {
       type = lib.types.str;
-      default = "";
+      default = schema.home.wallpaper;
       description = "System wallpaper path.";
     };
     panelPosition = lib.mkOption {
       type = lib.types.enum [ "top" "bottom" ];
-      default = "top";
+      default = schema.home.panelPosition;
       description = "Waybar panel position.";
     };
     hyprland = {
       gaps_in = lib.mkOption {
         type = lib.types.int;
-        default = 5;
+        default = schema.home.hyprland.gaps_in;
         description = "Inner gaps for Hyprland.";
       };
       gaps_out = lib.mkOption {
         type = lib.types.int;
-        default = 10;
+        default = schema.home.hyprland.gaps_out;
         description = "Outer gaps for Hyprland.";
       };
       border_size = lib.mkOption {
         type = lib.types.int;
-        default = 2;
+        default = schema.home.hyprland.border_size;
         description = "Border size for Hyprland.";
       };
     };
     fonts = {
       monospace = lib.mkOption {
         type = lib.types.str;
-        default = "JetBrainsMono Nerd Font";
+        default = schema.home.font;
         description = "System monospace font.";
       };
     };