Herdr children — offload, merge, then remove

Standing rule for a manager session on a repo that uses Herdr worktrees:

• Offload implementation to child worktrees. Resume dead sessions in small batches so the host stays usable. Do not implement features in the manager checkout.
• Heavy Node work runs once, in the manager session: local-ci, typecheck, vitest, assets:build, and app builds. Children do not run those in parallel.
• Group edits that touch the same files into one child. Split only independent work.
• When a child PR is ready, squash-merge it onto the repo's default branch, then remove that worktree.
• Leave a lane whose agent is still working, and any tree with uncommitted work that is not already on the default branch.
• Do not merge release-please or dependency-bump PRs (feedback-never-auto-merge-release-please).

Why: The user repeats this as the manager loop: children build, the manager integrates, finished checkouts go away.

How to apply: On each manager turn, list child worktrees, resume or spawn the unfinished ones, merge only gated PRs, and reclaim only landed trees.