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.

nix/host-modules/hive-c0re/environment.nix

@@ -208,6 +208,13 @@ in
   # forge links rather than emitting one it can't justify.
   HIVE_FORGE_PUBLIC_URL = config.services.hyperhive.swarm.forge.publicUrl;
 }
+// lib.optionalAttrs (config.services.hyperhive.swarm.domain != null) {
+  # Browser URL of the swarm UI, which answers on the swarm apex domain
+  # (see ../swarm-ui.nix). The dashboard links to it from its pages menu.
+  # Absent when the domain is unset, so the link is hidden rather than
+  # guessed.
+  HIVE_SWARM_PUBLIC_URL = "https://${config.services.hyperhive.swarm.domain}/";
+}
 // lib.optionalAttrs (config.services.hyperhive.swarm.matrix.gatewayHost != null) {
   # Browser-facing matrix GUI (fluffychat) URL — the gateway
   # vhost (`gatewayHost`, `chat.<swarm-domain>` by default). Surfaced via the daemon's `Urls`

nix/host-modules/hive-forge/service.nix

@@ -116,13 +116,13 @@ in
       example = "https://forge.example.com";
       description = ''
         Browser-facing forge URL the dashboard uses to build clickable
-        forge links (the H0M3 Forge tile, per-agent-row forge links) —
+        forge links (the per-agent-row forge links) —
         sourced into every agent container + hive-c0re as
         `HIVE_FORGE_PUBLIC_URL`.
 
         Defaults to `https://''${cfg.domain}`, the gateway vhost. When
         `null`, the dashboard **hides** forge links rather than
-        guessing one — see `docs/web-ui/dashboard.md::H0M3 page` for
+        guessing one — see `docs/web-ui/dashboard.md::Container row` for
         the rationale (a link built from the operator's own browser
         hostname + a container port is only an accident away from
         wrong on any deployment that isn't plain localhost).

nix/host-modules/hive-gateway/vhosts.nix

@@ -192,7 +192,7 @@ let
   # files — hive-c0re serves none of this as a fallback.
   # `= /api/docs` (no trailing slash) redirects to `/api/docs/`: nginx
   # owns that redirect because hive-c0re has no route for it, and the
-  # H0M3 hub's own `/api/docs` link (no trailing slash) would 404
+  # the dashboard's own `/api/docs` links (no trailing slash) would 404
   # without it.
   swaggerUiLocations = {
     "= /api/docs" = {