boundary.md keeps the model, the design rule, why network isolation
matters and host admin socket access; the hive-priv socket activation and
the per-agent socket directory move to 4-implementation/trust-boundary.
security.md keeps the agent trust model and the path-name rule; the nix
builds mode with its threat model, and the hive-c0re privilege separation,
move to their own pages there. Headings and text move as they were, with
one level shaved off the heading depth. Links, code and nix pointers, and
the docs index follow the moves.
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.
