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.

pkgs/nomarchy-install/default.nix

@@ -17,7 +17,7 @@
 , btrfs-progs      # inspect-internal map-swapfile (hibernation offset)
 , xkeyboard_config # human-readable installed layout/variant catalog
   # Baked metadata — what this installer installs and where it came from.
-, templateDir              # templates/downstream (home.nix, theme-state.json)
+, templateDir              # templates/downstream (home.nix, state.json)
 , nomarchyLock             # the distro's flake.lock (for offline lock composition)
 , hardwareModuleNames      # newline-separated nixos-hardware module names
 , nixpkgsPath              # pinned nixpkgs source (NIX_PATH for disko's eval)
@@ -54,7 +54,7 @@ stdenvNoCC.mkDerivation {
     mkdir -p "$share/template"
     # Full downstream template is the SoT; install script copies + patches.
     cp ${templateDir}/flake.nix ${templateDir}/system.nix \
-       ${templateDir}/home.nix ${templateDir}/theme-state.json \
+       ${templateDir}/home.nix ${templateDir}/state.json \
        "$share/template/"
     install -Dm644 patch-template.py "$share/patch-template.py"