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/idle.nix

@@ -1,5 +1,5 @@
 # hyprlock + hypridle — screen locking and idle management, themed from
-# theme-state.json. One concern, one file: hypridle drives WHEN (idle
+# state.json. One concern, one file: hypridle drives WHEN (idle
 # lock, display off, suspend, lock-before-sleep), hyprlock is the
 # themed lock screen itself (also behind the power menu's Lock entry).
 { config, lib, pkgs, ... }: