banner for deep research course (#158)

publish at 10AM PT

Author: lnhsingh

src/docs.json

@@ -97,6 +97,9 @@
   "styles": [
     "/hide-version-picker.css"
   ],
+  "banner": {
+    "content": "Our new LangChain Academy Course Deep Research with LangGraph is now live! [Enroll for free](https://academy.langchain.com/courses/deep-research-with-langgraph/?utm_medium=internal&utm_source=docs&utm_campaign=q3-2025_deep-research-course_co)."
+  },
   "navigation": {
     "global": {
       "anchors": [