dashboard: inline the frost background fallback and fix a stale flow-page reference

The frost variable was defined only in the removed flow stylesheet, so its
fallback always applied. The messages page header no longer points at the
flow page.

frontend/packages/dashboard/src/dashboard.css

@@ -617,10 +617,7 @@ footer .banner-thin {
   flex-wrap: wrap;
   gap: 0.6em;
   padding: 0.55em 1em;
-  background: var(
-    --flow-frost-bg,
-    color-mix(in srgb, var(--bg) 74%, transparent)
-  );
+  background: color-mix(in srgb, var(--bg) 74%, transparent);
   -webkit-backdrop-filter: blur(12px) saturate(140%);
   backdrop-filter: blur(12px) saturate(140%);
   border-top: 1px solid var(--purple);

frontend/packages/swarm-ui/src/pages/messages/MessagesPage.tsx

@@ -1,7 +1,6 @@
 // <MessagesPage> — `/messages`: every message between agents, and from the
 // operator, reminders and compaction to an agent, as the swarm's controller
-// streams them (`GET /api/messages/stream`). The read side of the hive
-// dashboard's flow page, across all hives.
+// streams them (`GET /api/messages/stream`), across all hives.
 //
 // The stream sends the chosen window of history first, then the live tail. A
 // message an agent drained with an in-turn `recv` is missing, because it starts