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/home/first-boot.nix

@@ -32,7 +32,7 @@
         Environment = [
           "PATH=${lib.makeBinPath [
             pkgs.libnotify
-            pkgs.nomarchy-theme-sync
+            pkgs.nomarchy-state-sync
             pkgs.coreutils
           ]}"
           "NOMARCHY_PATH=%h/.nomarchy"