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.

agent/BACKLOG.md

@@ -226,7 +226,7 @@ always — the same on-AC question `modules/home/idle.nix`'s suspend listener
 already answers with `${onAc} ||`.
 
 In-flake state like the rest (`settings.*`), menu-writable, and read via
-`theme-state-read.nix` on the NixOS side — NOT `config.nomarchy.settings`,
+`state-read.nix` on the NixOS side — NOT `config.nomarchy.settings`,
 which does not exist there (ROADMAP § *NixOS-side state bridges (#116)*; copy
 the `bluetooth.enable` shape in `modules/nixos/default.nix` and add a case to
 `checks.state-bridges`). Pass = the toggle survives a rebuild,
@@ -234,22 +234,6 @@ a suspended machine hibernates after the configured delay and resumes, and a
 machine without hibernate support hides the row instead of offering a
 suspend that never wakes.
 
-### 107. Rename `theme.json` to reflect that it is the system state
-
-The state file long ago stopped being about themes: it carries night-light,
-keyboard memory, display resolution and profiles, auto-commit, services and
-more, so `theme.json` now misnames its own contents and misleads anyone
-reading the flake. Rename it to `state.json` (Bernardo's call, 2026-07-14 —
-settled, do not revisit), and carry the `nomarchy-theme-sync` tool name along
-with it.
-
-Standalone task — do not fold it into a feature. Ships with a compatibility
-shim that keeps reading an existing `theme.json` so downstream checkouts do
-not break on a pull, plus a migration note. Pass = a fresh install and an
-existing downstream checkout both work, every in-repo reference (modules,
-tools, template, docs) uses the new name, and the shim is documented with the
-release it can be dropped in.
-
 ### 104. Runtime Airplane mode
 
 Add Airplane mode under System connectivity controls. It must disable Wi-Fi
@@ -280,7 +264,7 @@ read, so *these two toggles have never actually worked for any user*. That
 cuts both ways: "preserve existing behavior" is not a reason to keep them
 (there is no behavior to preserve), but the state keys and their bridges are
 real now and outlive the TUI — dropping the rows must not drop the keys, or a
-machine whose theme-state.json already says `bluetooth.enable = false` will
+machine whose state.json already says `bluetooth.enable = false` will
 silently flip back on at the next rebuild. `checks.state-bridges` covers those
 two keys and will fail loudly if the bridges go with the tool; keep it green,
 and if a key is deliberately retired, remove its case in the same commit.