Give the root tools to start and message children

The root creates permanent children with its model and effort, sends
them durable messages with tell, and reads their views with zoom. A
child has a short capitalized name for its area, such as House, which no
child, subagent, or the root uses. spawn keeps its short tasks. Children
have no creation or WhatsApp tools.

The root sees each child name and area in its turn state, while its
shared prompt stays stable. The prompt directs mixed-chat area messages
to the right child with their sender, date, and words, and requires user
agreement before the root sends a child draft to WhatsApp.

A new child is prepared outside the children directory and published in
one step, so a stop never leaves a half-made child that blocks the next
start, and a failed creation frees its name. Runtime children join the
daemon lifetime and backup locks before they receive tasks.

Issue: 63b101c