fix(state): auto-commit died on dead legacy pathspecs after #107

Since d8e1a13 removed theme-state.json, auto_commit's fixed pathspec
(state.json + both legacy names) made `git commit` abort — unlike
`git diff`, commit errors on a pathspec that matches nothing — so every
per-mutation settings commit was silently "skipped" and state.json
stayed dirty until a lifecycle sweep caught it. Filter the legacy names
down to those git still knows (index or HEAD — a migration's staged
`git rm` still rides along). checks.auto-theme now runs its state dir
as a git repo with autoCommit on and asserts each set/apply lands as
its own commit leaving nothing dirty — the exact post-#107 repo shape
that used to abort. state-sync 0.5.0 → 0.5.1.

V2: nix build .#checks.x86_64-linux.auto-theme (KVM VM run, passed,
including the new git assertions); the built tool was also exercised
against a clone of a real post-#107 machine flake — the set
auto-committed and the tree stayed clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkgs/nomarchy-state-sync/default.nix

@@ -16,7 +16,7 @@
 
 stdenvNoCC.mkDerivation {
   pname = "nomarchy-state-sync";
-  version = "0.5.0";
+  version = "0.5.1";
 
   src = ./.;