dashboard: serve the dashboard at /, fold kept state in as a tab, add a pages menu

Drop the H0M3 tile hub and the core page. The dashboard is now the index;
kept state is its fifth tab. A pages menu in the chrome links flow, stats,
API docs and the swarm UI. The swarm apex URL comes from
services.hyperhive.swarm.domain via HIVE_SWARM_PUBLIC_URL and the new
swarm_public_url field of the state snapshot.

frontend/packages/swarm-ui/src/shell/LinksMenu.tsx

@@ -9,8 +9,8 @@
 // The list is entirely server-driven (see swarm-controller's
 // `services.hyperhive.swarm.controller.links` option) — 0 entries
 // hides the button rather than showing an empty popover, same "don't
-// render a dead affordance" rule the old dashboard's H0M3 tiles follow
-// for Forge/Matrix.
+// render a dead affordance" rule the dashboard's pages menu follows for
+// its swarm entry.
 import { useEffect, useRef, useState } from "preact/hooks";
 import { LinkIcon } from "@hive/shared/icons.js";
 import "./LinksMenu.css";

frontend/packages/swarm-ui/src/shell/MatrixRain.tsx

@@ -5,8 +5,7 @@
 // Stepped on an interval (the steppy cadence is the look, and it costs
 // little), paused while the tab is hidden, and stopped (and cleared) when
 // motion is reduced: the settings menu's `data-motion` override wins over
-// `prefers-reduced-motion`, and is followed live. The same effect as the hive dashboard's home
-// page, which is plain JS over a fixed canvas.
+// `prefers-reduced-motion`, and is followed live.
 import { useEffect, useRef } from "preact/hooks";
 import {
   CELL,