Wire a fifth pull hook so peer messages also surface between todo
items, not only at user prompts and subagent stops. While here,
extend the manual `install-hook` CLI so it patches the full plugin
hook set (SessionStart/UserPromptSubmit/SubagentStop/TaskCompleted/
SessionEnd) instead of only UserPromptSubmit, mirroring what the
plugin's hooks.json registers. Mailbox name is auto-derived from
stdin, so --name is no longer required.
Also corrects stale docs that claimed SessionStart auto-bootstraps
the watcher — push delivery has been opt-in since the
mailbox-collaborate skill landed.
3ebf54e75d