feat(dashboard): add morning brief preview and test-send action

docs/plans/state.json

@@ -5480,6 +5480,19 @@
         "docs/plans/state.json"
       ],
       "test_status": "pnpm typecheck passing"
+    },
+    "dashboard-morning-brief-preview-test-send": {
+      "status": "completed",
+      "date": "2026-02-18",
+      "updated": "2026-02-18",
+      "summary": "Extended Dashboard Assistant Health with a Morning Brief Preview panel (prompt/schedule/tier/output metadata) and a one-click Test Briefing action that triggers the configured daily briefing via cron.trigger through gateway tools.invoke, including inline save/trigger status feedback.",
+      "files_modified": [
+        "src/gateway/ui/pages/dashboard.js",
+        "src/gateway/ui/style.css",
+        "README.md",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm typecheck passing"
     }
   },
   "overall_progress": {