fix(theme): #66 fail-closed theme-state errors at mkFlake/read

Missing, empty, or non-object theme-state.json now throws a short
message pointing at the template and `nomarchy-theme-sync validate`
instead of a raw readFile/fromJSON stack. Shared reader:
modules/theme-state-read.nix — wired in theme.nix, plymouth/timezone/
hardware, and lib.mkFlake (seq-forced early gate). Field-level schema
in theme.nix kept; unknown border roles still fail there; resolveColor
no longer falls through on missing palette keys. Defaults added for
settings.displayProfile / displayProfileAuto.

Verified: V0 nix flake check --no-build; negative evals (missing,
empty, [], bad border role); good-path template mode + displayProfile
defaults.

lib.nix

@@ -5,7 +5,16 @@
 # in flake.nix remain the escape hatch for power users.
 { nixpkgs, home-manager, nixos-hardware, nomarchy }:
 
+let
+  inherit (nixpkgs) lib;
+
+  # Shared pure reader (modules/theme-state-read.nix) — re-exported so
+  # power users composing without mkFlake can call it too.
+  readThemeState = import ./modules/theme-state-read.nix { inherit lib; };
+in
 {
+  inherit readThemeState;
+
   mkFlake =
     { src                      # the downstream flake directory (./.)
     , username                 # login name; also the homeConfigurations attr
@@ -13,8 +22,6 @@
     , system ? "x86_64-linux"
     }:
     let
-      inherit (nixpkgs) lib;
-
       # One profile or several (the installer's autodetection emits a few
       # common-* modules alongside the model-specific one).
       profileNames =
@@ -51,8 +58,17 @@
         # and the standalone HM desktop see the same package set.
         config.allowUnfree = true;
       };
+
+      # Early fail-closed gate: missing/empty/non-object theme-state.json
+      # throws here with a template + validate pointer, before module
+      # evaluation buries a raw readFile/fromJSON stack. Field-level
+      # schema still runs in modules/home/theme.nix after defaults merge.
+      # Forced via seq on the whole return set — attrNames alone must not
+      # skip the check (Nix is lazy on unused let bindings and attr values).
+      statePath = src + "/theme-state.json";
+      _themeState = readThemeState statePath;
     in
-    {
+    builtins.seq _themeState {
       # System layer — rebuilt rarely:
       #   sudo nixos-rebuild switch --flake .#default
       nixosConfigurations.default = nixpkgs.lib.nixosSystem {
@@ -67,7 +83,7 @@
             { environment.systemPackages = [ home-manager.packages.${system}.home-manager ]; }
             # System-side theme consumers (Plymouth splash background)
             # read the same JSON the desktop does.
-            { nomarchy.system.stateFile = src + "/theme-state.json"; }
+            { nomarchy.system.stateFile = statePath; }
           ]
           ++ hardwareModules
           ++ [
@@ -87,7 +103,7 @@
           {
             # Written by nomarchy-theme-sync; reading it is pure — the
             # file is part of the downstream flake's source.
-            nomarchy.stateFile = src + "/theme-state.json";
+            nomarchy.stateFile = statePath;
             home = {
               inherit username;
               homeDirectory = "/home/${username}";