Adds a lefthook `pre-push` job that runs the same checks as CI
code-quality (`oxfmt --check .` + `oxlint .`), so formatting/lint
failures are caught locally before they reach a PR. Uses the existing
lefthook setup - no new tooling.
Caveat noted in the config: GitButler uses its own git implementation
and only runs hooks when "Run hooks" is enabled in its per-project
settings; with that off, this protects plain `git push`. Enable that
setting to have it fire on `but push` too.
nicktrn