fix: view-queue link + agent inbox shows unread messages only

fix(dashboard): update 'view queue' link to /builds.html

The build queue moved to its own /builds.html page. The queue-summary
'view queue →' link in tabs.js still pointed at /core.html, so clicking
it landed on the wrong page.

fix(broker): filter agent inbox to unread (acked_at IS NULL)

recent_for was returning all messages regardless of ack state, so the
agent inbox showed everything even after 'mark all read'. Now filters
to acked_at IS NULL — mirroring exactly what mark_all_read drains —
so the inbox empties on reload after the operator drains it.

frontend/packages/agent/src/app.js

@@ -1133,11 +1133,9 @@ window.marked = marked;
       return wrap;
     }
     // "mark all read" header row drains the host broker's pending +
-    // delivered-unacked rows for this agent. Visible rows here are
-    // the most-recent-N regardless of ack state, so the list itself
-    // doesn't visually empty on click — the status pill confirms
-    // the drain count, and the next turn_start's "unread" badge
-    // will read zero.
+    // delivered-unacked rows for this agent. The inbox shows only
+    // unread (acked_at IS NULL) rows, so after the drain + refreshState()
+    // the list empties (matching the operator's expectation).
     wrap.append(buildInboxMarkAllRow(currentLabel, () => {
       // Refresh state so any UI surface that DOES depend on
       // delivery state (eg future per-status filters) picks up