Three tests for launch:
- creates worktree dir + branch off master
- ResetIfExists=true on existing branch+worktree succeeds
- returns Error when required args missing
Two tests for cleanup:
- removes worktree dir and branch after launch
- tolerates missing worktree/branch (cleanup called twice)
Uses initDummyRepo helper with isolated GIT_CONFIG_GLOBAL=/dev/null
so tests do not pick up user's signing/template config. Echo stub
fallback (claude not in PATH) keeps tests hermetic.
