The coordinator had no tool to add a worker, so a request to create one
fell back to update_workspace and wrote a bot that did not exist into the
workspace context. create_bot now adds a worker with its name, role and
instructions and joins it to a workspace, and add_bot_to_workspace puts an
existing worker in one. Both are coordinator-only and chat-replies-only,
and createBot still enforces the crew-manager check.
The coordinator's prompts now say how a bot gets created, and that one
which does not exist is never written into workspace context.
pick-free-hue moves to utils so the tool can pick a hue without importing
from layouts.
