v0.4.1 — trailing-slash fix

Fixes

• stitch add with a trailing slash now works. stitch add ~/.config/alacritty/
  used to fail at the link step with a confusing rollback error. Root cause:
  symlink(2) rejects a linkpath with a trailing slash (the kernel treats it as
  "must resolve to an existing directory", but the path doesn't exist yet when
  we're creating the symlink). expand_home now strips trailing slashes from
  its result, fixing the issue for every caller (add, apply, scan,
  config load). Root (/) is preserved.