fix(shell-docs): point Deep Agents CTA at /deepagents and add legacy redirects

The whats-new/langgraph-deep-agents CTA pointed at /langgraph/deep-agents,
which 404s. With the placeholder now live at /deepagents, re-point the
CTA there and add LEGACY_CHAINS_EXACT entries so old upstream URLs
(/langgraph/deep-agents and /langgraph-python/deep-agents) redirect to
the canonical /deepagents placeholder.

Supersedes the standalone CTA-removal PR CopilotKit#4832; this commit consolidates
that fix into the backport PR so a single PR covers all Deep Agents
URL wiring.

Author: samjulien

showcase/shell-docs/src/content/docs/whats-new/langgraph-deep-agents.mdx

@@ -27,7 +27,7 @@ CopilotKit brings your Deep Agents to the frontend. Users can see the agent's th
 
 ### Get Started
 
-- [Deep Agents Guide](/langgraph/deep-agents)
+- [Deep Agents Guide](/deepagents)
 
 </div>
 </div>

showcase/shell-docs/src/lib/seo-redirects.ts

@@ -535,6 +535,21 @@ const LEGACY_CHAINS_EXACT: RedirectEntry[] = [
     source: "/coagents/videos",
     destination: "/langgraph-python/videos",
   },
+  // Deep Agents was promoted from a langgraph subpath to its own
+  // top-level integration. Catch the legacy (langgraph) and the
+  // post-slug-rename (langgraph-python) variants both, pointing them at
+  // the canonical /deepagents placeholder. When the showcase
+  // integration ships, these targets continue to resolve unchanged.
+  {
+    id: "L12",
+    source: "/langgraph/deep-agents",
+    destination: "/deepagents",
+  },
+  {
+    id: "L13",
+    source: "/langgraph-python/deep-agents",
+    destination: "/deepagents",
+  },
 ];
 
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