refactor(#107): theme-state.json → state.json, theme-sync → state-sync

The machine flake's git-tracked settings file is system state, not
"theme" only — rename it to state.json. CLI becomes nomarchy-state-sync
with a nomarchy-theme-sync symlink for scripts and muscle memory.

Eval (mkFlake, doctor, lifecycle) still accepts theme-state.json; the
next write migrates to state.json and removes the legacy file.
Documented in MIGRATION.md; drop the CLI alias after release notes.

lib.nix

@@ -1,5 +1,5 @@
 # Downstream sugar: one call wires a whole machine flake.
-# Users own ONLY system.nix, home.nix and theme-state.json; their flake.nix
+# Users own ONLY system.nix, home.nix and state.json; their flake.nix
 # is generated once (by `nix flake init -t` or the future installer) and
 # never hand-edited. The raw exports (nixosModules/homeModules/overlays)
 # in flake.nix remain the escape hatch for power users.
@@ -8,9 +8,9 @@
 let
   inherit (nixpkgs) lib;
 
-  # Shared pure reader (modules/theme-state-read.nix) — re-exported so
+  # Shared pure reader (modules/state-read.nix) — re-exported so
   # power users composing without mkFlake can call it too.
-  readThemeState = import ./modules/theme-state-read.nix { inherit lib; };
+  readThemeState = import ./modules/state-read.nix { inherit lib; };
 in
 {
   inherit readThemeState;
@@ -59,13 +59,18 @@ in
         config.allowUnfree = true;
       };
 
-      # Early fail-closed gate: missing/empty/non-object theme-state.json
+      # Early fail-closed gate: missing/empty/non-object 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";
+      # #107: prefer state.json; accept legacy theme-state.json until
+      # the user's next menu write migrates them.
+      statePath =
+        if builtins.pathExists (src + "/state.json") then src + "/state.json"
+        else if builtins.pathExists (src + "/theme-state.json") then src + "/theme-state.json"
+        else src + "/state.json";
       _themeState = readThemeState statePath;
     in
     builtins.seq _themeState {
@@ -78,7 +83,7 @@ in
           [
             nomarchy.nixosModules.nomarchy
             # The standalone HM CLI ships with the system so theme switching
-            # (`nomarchy-theme-sync apply` → `home-manager switch`) works
+            # (`nomarchy-state-sync apply` → `home-manager switch`) works
             # out of the box — same pinned input as the desktop modules.
             { environment.systemPackages = [ home-manager.packages.${system}.home-manager ]; }
             # System-side theme consumers (Plymouth splash background)
@@ -94,14 +99,14 @@ in
 
       # Desktop layer — every theme change, no sudo:
       #   home-manager switch --flake .#<username>
-      # (`nomarchy-theme-sync apply` runs this for you.)
+      # (`nomarchy-state-sync apply` runs this for you.)
       homeConfigurations.${username} = home-manager.lib.homeManagerConfiguration {
         inherit pkgs;
         modules = [
           nomarchy.homeModules.nomarchy
           (src + "/home.nix")
           {
-            # Written by nomarchy-theme-sync; reading it is pure — the
+            # Written by nomarchy-state-sync; reading it is pure — the
             # file is part of the downstream flake's source.
             nomarchy.stateFile = statePath;
             home = {