fix(create): add .claude/worktrees/ to monorepo template gitignore (#1125)

## Summary

- Add `.claude/worktrees/` to the monorepo template's `_gitignore` so
that projects created with `vp create` ignore Claude Code worktree files
by default
- This prevents oxlint/oxfmt from reporting false warnings on worktree
files, since both tools respect `.gitignore` via the `ignore` crate's
`WalkBuilder`

Closes #1106

Author: jong-kyung

packages/cli/templates/monorepo/_gitignore

@@ -22,3 +22,6 @@ dist-ssr
 *.njsproj
 *.sln
 *.sw?
+
+# AI agent worktrees
+.claude/worktrees/