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.

modules/nixos/greeter.nix

@@ -1,4 +1,4 @@
-# Greeter — greetd/tuigreet, themed from the same theme-state.json that
+# Greeter — greetd/tuigreet, themed from the same state.json that
 # drives the desktop (nomarchy.system.stateFile; the Plymouth model:
 # baked at SYSTEM rebuild, so it follows the theme as of the last
 # sys-update, not the last instant apply).
@@ -27,7 +27,7 @@ let
   cfg = config.nomarchy.system;
   distroName = config.system.nixos.distroName;
 
-  sync = lib.getExe pkgs.nomarchy-theme-sync;
+  sync = lib.getExe pkgs.nomarchy-state-sync;
 
   # Menu/CLI toggle, same shape as nomarchy-autotimezone: runs as the normal
   # user (it owns the flake checkout + writes the state), sudos only the
@@ -62,12 +62,12 @@ let
     fi
   '';
 
-  # Fails closed with an actionable message via theme-state-read.nix, like
+  # Fails closed with an actionable message via state-read.nix, like
   # every other stateFile consumer — a raw fromJSON here would bury a bad
   # state file under a Nix stack pointing at greeter.nix.
   state =
     if cfg.stateFile != null
-    then import ../theme-state-read.nix { inherit lib; } cfg.stateFile
+    then import ../state-read.nix { inherit lib; } cfg.stateFile
     else { };
 
   # The auto-login user from the state, or null. Read here via the state file