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.

tools/check-template-sot.py

@@ -11,7 +11,7 @@ flake seed files (see pkgs/nomarchy-install/default.nix installPhase).
 
 The package copies a fixed file list (not a recursive tree copy):
 
-    flake.nix  system.nix  home.nix  theme-state.json
+    flake.nix  system.nix  home.nix  state.json
 
 README.md and hardware-configuration.nix stay repo-only (docs /
 nixos-generate-config at install time) and are intentionally absent
@@ -31,7 +31,7 @@ import sys
 from pathlib import Path
 
 # Must match the cp list in pkgs/nomarchy-install/default.nix installPhase.
-SHIPPED = ("flake.nix", "system.nix", "home.nix", "theme-state.json")
+SHIPPED = ("flake.nix", "system.nix", "home.nix", "state.json")
 
 
 def fail(msg: str) -> None: