Move the default session-worktree base from a repo sibling
(<repoParent>/.nucleic-worktrees/<repoSlug>) to inside the project at
<repoRoot>/.nucleic/worktrees. On first worktree creation, add .nucleic/
to the repo's local .git/info/exclude so the user's primary checkout
never reports it as untracked and the tracked .gitignore is untouched.
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>