docs: update banner with docs deprecation notice (#8893)

Author: lnhsingh

docs/core_docs/docusaurus.config.js

@@ -147,8 +147,8 @@ const config = {
       },
       announcementBar: {
         content:
-          'Our new LangChain Academy Course Deep Research with LangGraph is now live! <a href="https://academy.langchain.com/courses/deep-research-with-langgraph/?utm_medium=internal&utm_source=docs&utm_campaign=q3-2025_deep-research-course_co" target="_blank">Enroll for free</a>.',
-        backgroundColor: "#d0c9fe",
+          "These docs will be deprecated and no longer maintained with the release of LangChain v1.0 in October 2025. <a href='https://docs.langchain.com/oss/javascript/langchain/overview' target='_blank'>Visit the v1.0 alpha docs</a>",
+        backgroundColor: "#CC5500",
       },
       prism: {
         theme: {