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.

templates/downstream/home.nix

@@ -29,10 +29,10 @@
   #
   # Icon pack: Papirus ships by default (auto Dark/Light by theme mode) and
   # is the ONLY icon pack in your closure. To use another, set the `icons`
-  # field in your theme-state.json to a theme name from a known pack — only
+  # field in your state.json to a theme name from a known pack — only
   # that pack is then added (no bloat otherwise). Known packs: Papirus,
   # Tela, Qogir, Reversal, Numix (see modules/home/theme.nix `iconPacks`).
-  # e.g. theme-state.json:  "icons": "Tela-dark"
+  # e.g. state.json:  "icons": "Tela-dark"
 
   # ── Opt-in features — uncomment and tweak to enable ─────────────────
   # nomarchy.nightlight = {             # scheduled blue-light filter (hyprsunset)