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.

frontend/packages/agent/src/agent.css

@@ -16,7 +16,7 @@
 
 /* ─── full-screen layout overrides ─────────────────────────────────
    The agent page mounts a full-viewport terminal under a fixed
-   frosted-glass header. See docs/2-handbook/web-ui/agent.md::Per-agent
+   frosted-glass header. See docs/2-handbook/agents/web-page.md::Per-agent
    page for the layer / pill / side-panel structure; rules below
    override the in-page defaults from @hive/shared. */
 
@@ -184,7 +184,7 @@ h3 {
 }
 .agent-icon {
   /* Square identity anchor — explicit 5em sizing + align-self.
-     See docs/2-handbook/web-ui/agent.md::Per-agent page (Agent icon) for the
+     See docs/2-handbook/agents/web-page.md::Per-agent page (Agent icon) for the
      intrinsic-dim-pushes-parent-flex-open + sticks-to-top
      rationale. */
   width: 5em;
@@ -594,7 +594,7 @@ pre.diff {
 /* Tail pill (↓ N new): z-index bumped above the floating chrome so the
    pill sits on the top layer instead of being clipped by it. (Pill is anchored in
    `.agent-main` rather than `.terminal-wrap` — see
-   docs/2-handbook/web-ui/agent.md::Per-agent page Terminal-wrap paragraph for the
+   docs/2-handbook/agents/web-page.md::Per-agent page Terminal-wrap paragraph for the
    backdrop-filter stacking-context rationale.) */
 .agent-main .tail-pill {
   bottom: 0.6em;

frontend/packages/agent/src/components/Header.tsx

@@ -50,7 +50,7 @@ export interface HeaderProps {
    * a variable pill count) grows to fit badges+pills together, keeping
    * the header a stable height even on widescreen. Meta-nav
    * (`<MetaNav>`) lives here too, as a fixed-size trigger, not an
-   * inline link list in the title row (docs/2-handbook/web-ui/agent.md). */
+   * inline link list in the title row (docs/2-handbook/agents/web-page.md). */
   pills?: ComponentChildren;
 }
 

frontend/packages/agent/src/index.html

@@ -19,7 +19,7 @@
   <body class="agent-shell">
     <!-- The Preact rewrite owns everything below — header, terminal,
        side panel. See main.tsx/Root.tsx for the component
-       tree; docs/2-handbook/web-ui/agent.md for the design. -->
+       tree; docs/2-handbook/agents/web-page.md for the design. -->
     <div id="preact-root"></div>
 
     <script type="module" src="static/main.js" defer></script>

frontend/packages/agent/src/screen.html

@@ -36,7 +36,7 @@
     <script>
       // Minimal RFB-over-WebSocket renderer. Connects to `screen/ws` on
       // the same host; the harness relays raw RFB bytes to the VNC server
-      // running inside the container. See docs/2-handbook/web-ui/agent.md (GET /screen)
+      // running inside the container. See docs/2-handbook/agents/web-page.md (GET /screen)
       // for the design rationale + canvas-sizing implementation notes.
 
       (function () {
@@ -61,7 +61,7 @@
         });
 
         // --- Fit-to-window toggle ---
-        // See docs/2-handbook/web-ui/agent.md::Per-agent endpoints (GET /screen) for the
+        // See docs/2-handbook/agents/web-page.md::Per-agent endpoints (GET /screen) for the
         // localStorage persistence + canvas-intrinsic-resolution +
         // pointer-rescale model.
         let fitMode = localStorage.getItem("screen-fit") !== "off";
@@ -105,7 +105,7 @@
         // Sends an RFB SetDesktopSize request so the VNC server (weston)
         // changes its actual output resolution to match the browser
         // viewport — sharper than fit-mode's CSS downscale. Gated on the
-        // server's ExtendedDesktopSize advert; see docs/2-handbook/web-ui/agent.md::Per-agent
+        // server's ExtendedDesktopSize advert; see docs/2-handbook/agents/web-page.md::Per-agent
         // endpoints (GET /screen).
         let extDesktopSupported = false;
         let screenId = 1; // captured from the server's ExtendedDesktopSize advert

frontend/packages/agent/src/types.ts

@@ -35,7 +35,7 @@ export interface AgentState {
 // in the agent page header (stats/screen/forge/config + any
 // `services.hyperhive.agent.dashboardLinks` extras). `agent_links()` on the backend
 // is the single source of truth for what links an agent exposes; see
-// docs/2-handbook/web-ui/agent.md::Header for the kind → URL resolution table.
+// docs/2-handbook/agents/web-page.md::Header for the kind → URL resolution table.
 export interface AgentLink {
   url: string;
   icon: string;