Spawn Worktree Agent

This skill turns the current session into a launcher: it does NOT solve the problem itself. It creates an isolated worktree, starts an autonomous worker there with a specialized prompt, and reports. The real work happens in the worker.

Prerequisites (check first; stop with a clear message if unmet)

1. Running inside Herdr: HERDR_ENV is 1. If not, this skill does not apply — tell the user and stop.
2. herdr >= 0.7.5 (herdr --version). Older versions lack agent start --kind.
3. herdr, jq, lazygit on PATH. For the default claude kind, claude too; for --kind opencode, opencode.
4. The herdr-worktree skill is installed. If not, tell the user to install it and stop.
5. For --kind claude: the one-time --dangerously-skip-permissions bypass warning must have been accepted once on this machine, or the worker will wait at that prompt.

Step 1: Classify intent, agent kind, and branch