Wraps PUT /api/hives/{hive}/agents/{agent}/state, the route the swarm UI's
state menu uses. States come from swarm_wire::wanted::AgentState; destroyed
needs --yes.
Closes#6159
Every docs directory moves under 1-getting-started, 2-handbook,
4-implementation or 5-project; the options reference (section 3) comes from
the website and has no directory here. trust-boundary stays whole under the
handbook for now. web-ui, swarm and tools split between handbook and
implementation, and the command-line references move to
2-handbook/reference. Links, path references in code and nix, and the docs
index follow the moves; no page content changes.
