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/monitor-fallback.nix

@@ -41,7 +41,7 @@ pkgs.testers.runNixOSTest {
     nomarchy.system.stateFile = flake + "/themes/boreal.json";
     systemd.tmpfiles.rules = [
       "d /home/nomarchy/.nomarchy 0755 nomarchy users -"
-      "C /home/nomarchy/.nomarchy/theme-state.json 0644 nomarchy users - ${flake + "/themes/boreal.json"}"
+      "C /home/nomarchy/.nomarchy/state.json 0644 nomarchy users - ${flake + "/themes/boreal.json"}"
       "f /run/nomarchy-test-lid-state 0644 nomarchy users - state:_closed"
     ];
     services.greetd.settings.initial_session = {