Worktree tests fail on git builds that init on main

[gjjkbssg]

On a macOS developer machine with Apple Git (git 2.39+), make test fails in internal/worktree:

Test: TestRemoveAll
Messages: git -C ... checkout master failed: error: pathspec 'master' did not match any file(s) known to git

The suite is green on the Linux CI because the runner's git still initializes new repositories on "master", while Apple Git initializes "main" (the test helper already masks the global config with GIT_CONFIG_GLOBAL=/dev/null, so the built-in default is what leaks through). The tests hardcode checkout master even though the helper's own comment says the initial commit lands on main — clawk's primary platform is macOS, so every Mac dev hits this before their first contribution.

Fix is to pin the name at init (git init -b main) and check out main in both tests; then the suite is independent of the git build's default. I have the change ready and will open a PR referencing this issue.

[gjjkbssg]

Pinpointed the exact mechanism, in case it does not reproduce on your machine:

Apple's Xcode Command Line Tools ship a system-level gitconfig at /Library/Developer/CommandLineTools/usr/share/git-core/gitconfig that sets init.defaultBranch = main. The test helper masks only the global config (GIT_CONFIG_GLOBAL=/dev/null), so on any Mac with a recent CLT the fixture repo inits on main and the hardcoded checkout master fails. Older CLT versions don't ship that setting, which is likely why it never bit you.

GitHub's Ubuntu runners use stock git without that system config (built-in default master), which is why CI stays green while every recent-CLT Mac fails. git init -b main sidesteps the whole question of who sets what default.