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/swaync.nix

@@ -1,5 +1,5 @@
 # swaync — notification daemon + control centre, themed from
-# theme-state.json. Until this shipped, nothing rendered notify-send at
+# state.json. Until this shipped, nothing rendered notify-send at
 # all: the theme-switch progress toasts, the CLI's font warnings and the
 # live ISO's welcome message were all invisible.
 { config, lib, ... }:
@@ -29,7 +29,7 @@ in
       };
 
       style = ''
-        /* Palette baked from theme-state.json. Only roles guaranteed to
+        /* Palette baked from state.json. Only roles guaranteed to
            contrast @base in EVERY palette are used: subtext/surface mean
            "on-surface" in some light themes (summer-day: subtext==base,
            surface==text — body text was invisible on hardware, item 25).