WORKTREE_PATH polluted when auto-creating remote-only branch (track_mode=auto) #32

Summary

When creating a worktree in track_mode=auto for a branch that exists only on origin, stdout from git branch --track is mixed into create_worktree output. The returned WORKTREE_PATH becomes contaminated (e.g., starts with Branch 'foo' set up to track 'origin/foo'.), causing postCreate hooks to cd into the wrong path and fail.

Steps to Reproduce

1. Ensure branch exists on origin only: git ls-remote --heads origin <branch> (no local branch).
2. Run git gtr new <branch> (default track_mode=auto).
3. Inspect WORKTREE_PATH passed to postCreate hook or echo the function output.

Expected Behavior

create_worktree stdout contains only the worktree path; WORKTREE_PATH is a clean path and cd "$WORKTREE_PATH" succeeds.

Actual Behavior

git branch --track prints to stdout, which is concatenated with the path. postCreate hook receives a polluted value and cd $WORKTREE_PATH fails (interpreted as cd Branch etc.).

Environment

• Observed on: macOS (git 2.x, zsh)
• Affects: track_mode=auto with remote-only branches; local/none modes and existing local branches are not affected.

Proposed Fix

Redirect git branch --track "$branch" "origin/$branch" stdout (and stderr) to /dev/null in the auto branch creation path, keeping create_worktree stdout clean. A one-line change in lib/core.sh resolves the issue.