chore: remove accidentally-tracked runtime artifacts in impl/rust-cli/ (#75)

Two files slipped into the tree via #73 (cargo fmt sweep agent) when a
prior `vsh` test session left runtime state behind that `git add -A`
captured:

- `impl/rust-cli/$FILE` (5 bytes, literal "test\n") — the result of
  an unescaped `> $FILE` shell redirection
- `impl/rust-cli/.vsh_state.json` (414 bytes) — the vsh transaction
  history from that test session

Add `.vsh_state.json` and `$FILE` to root `.gitignore` so this can't
recur.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.gitignore

@@ -107,3 +107,8 @@ zig-out/
 # Crash recovery artifacts
 ai-cli-crash-capture/
 .cache/
+
+# vsh runtime state (sandbox transcript)
+.vsh_state.json
+# Accidental shell-redirect output from `> $FILE` testing
+$FILE