fix: base new worktrees on fetched origin/<default> instead of stale …

…local main (#5)

ygg new fetched origin but based worktrees on the stale local default branch. Now:
- Worktrees are based on the freshly fetched origin/<default> when it is ahead, else local (never dropping unpushed local commits); --no-track.
- ygg clean / ygg remove measure merge detection against the same resolved base.
- BaseRef returns fully-qualified refs (ambiguity-proof) with a friendly display name.
- ygg clean never schedules the default-branch worktree for removal.
- Removed dead Pull(); corrected help text; added tests.

fix: open zellij tabs in worktree dir on zellij 0.44+ (#2)

Zellij 0.44 stopped honoring `new-tab --cwd <path>` when no
INITIAL_COMMAND is supplied — the default shell starts in $HOME
regardless. Pass $SHELL (with /bin/sh fallback) as the initial command
so --cwd takes effect, plus --close-on-exit so the pane behaves like a
normal default-shell tab (closes on exit instead of respawning).

Merge pull request #1 from joch/add-skill

feat: add ygg skill install/uninstall for AI coding agents

fix: use separate tokens for release and Homebrew tap push

fix: match most specific worktree path in Current()

Since .worktrees is inside the repo root, the primary worktree path
is a prefix of all worktree paths. Use longest match to find the
correct current worktree.

feat: warn if .worktrees is not in .gitignore on create

feat: copy untracked files, merge checks, and rename worktree dir

- Copy untracked/gitignored files to new worktrees automatically
- Check for unmerged branches before removing worktrees
- Change worktree directory from .ygg-worktrees to .worktrees

fix: update CI workflow actions to latest versions