Builds on @hwantage's fix: `git -c core.longpaths=true` only helped the plain
`worktree add`, so two deep-path cases still failed with "Filename too long".
- Sparse creation: `worktree add --no-checkout` writes no files, so the flag
now also rides the `sparse-checkout set` and `checkout <branch>` calls that
actually materialize the tree. Without it the failure landed after the
worktree existed and rolled the whole create back.
- SSH: relay addWorktreeOp builds its own argv, so a Windows SSH host was
never covered. It now keys off the execution host's platform, not the
client's, and the hardcoded --no-checkout splice index is offset by the
prefix.
- Predicate is now the cwd (`\\wsl.localhost\...` opts out) rather than the
wslDistro option, which is not what decides which git binary runs.
Scope stays command-level `-c`; no user, repo, or system config is written.
