docs: the handbook follows the three layers: swarm, hives, agents

The handbook's sections were agent-lifecycle, integrations, swarm, tools,
trust-boundary and web-ui, which do not follow how the system is built, so a
reader could not tell which layer a page is about. Its pages now sit in
swarm/, hives/ and agents/, with the accounts an agent can hold outside the
system in external-accounts/.

- swarm/: forge, matrix and the knowledge repo join the swarm pages, and so
  does the swarmctl reference.
- hives/: the dashboard, hivectl and its reference, and the operator/agent
  boundary, with a README that takes over the old web-ui and tools pages.
- agents/: the roster, persistence, config changes, the agent's own web page
  (was web-ui/agent) and the security model, with a README.
- external-accounts/: GitHub and GitLab.

Pages are moved whole; none is split yet. Every reference follows: relative
links in the docs, `docs/2-handbook/...` paths in code comments, the nix
checks that regenerate the CLI references and the ignore list, and docs/README.md,
whose handbook section is now by layer.

docs/4-implementation/scheduler/coordinator.md

@@ -2,7 +2,7 @@
 
 Architecture notes for the `hive-c0re` coordinator daemon's internal subsystems.
 For the public API surface (dashboard, socket protocol) see `docs/5-project/process/conventions.md`
-and `docs/2-handbook/agent-lifecycle/persistence.md`.
+and `docs/2-handbook/agents/persistence.md`.
 
 ---
 
@@ -328,7 +328,7 @@ boot with no operator action in this process never finds drift of its own.
 
 Agents build from the swarm's `internal/meta` flake, which swarm-controller
 commits and the swarm builder builds from (see
-[Config changes](../../2-handbook/agent-lifecycle/config-changes.md#the-swarms-meta-flake)).
+[Config changes](../../2-handbook/agents/config-changes.md#the-swarms-meta-flake)).
 The hive keeps no flake of its own and deploys the closure the swarm builds
 from it, as the agent's `agent-closures` record declares (`attic/closure.rs`).
 `agent_set.rs` keeps the
@@ -536,7 +536,7 @@ config — all nspawn containers live in `machine.slice`.
 
 ## See also
 
-- `docs/2-handbook/agent-lifecycle/config-changes.md` — config PRs, meta flake, system messages
-- `docs/2-handbook/agent-lifecycle/persistence.md` — SQLite schema, state-dir layout
+- `docs/2-handbook/agents/config-changes.md` — config PRs, meta flake, system messages
+- `docs/2-handbook/agents/persistence.md` — SQLite schema, state-dir layout
 - `docs/5-project/process/conventions.md` — wire protocol, recipient sentinels
-- `docs/2-handbook/agent-lifecycle/agent-roster.md` — the agent roster and privilege
+- `docs/2-handbook/agents/agent-roster.md` — the agent roster and privilege

docs/4-implementation/scheduler/jobq.md

@@ -34,7 +34,7 @@ swarm controller and hive-c0re each build their own graph on it.
 Two views, one per graph, drawn by the same component: the swarm UI's
 `/jobs` page shows the swarm controller's graph, and the hive dashboard's
 **R3BU1LD QU3U3** tab (see
-[`2-handbook/web-ui/dashboard.md`](../../2-handbook/web-ui/dashboard.md)) shows that hive's. Each
+[`2-handbook/hives/dashboard.md`](../../2-handbook/hives/dashboard.md)) shows that hive's. Each
 **row** is one job; the rows nested under it are that job's steps, in
 order (occasionally a couple run side by side). A step shows one of:
 

docs/4-implementation/scheduler/observability.md

@@ -104,7 +104,7 @@ smuggled out in resource attributes on an otherwise-legitimate export.
 That's a **different risk from the one the collector fixes**: an agent that
 held the upstream credential could do everything above _and_ use the token
 anywhere else. The collector removes the token and keeps the pipe. Agents are inside the trust
-boundary (`docs/2-handbook/trust-boundary/security.md`: capability = accepted risk), so an agent being
+boundary (`docs/2-handbook/agents/security.md`: capability = accepted risk), so an agent being
 able to _send_ is an accepted extension of that boundary — but it's not
 closed by this design, and don't read anything here as closing it.