Upgrade Docusaurus from pinned canary to ^3.9.0

Unpin @docusaurus/* packages from 3.8.1-canary-6401 to ^3.9.0 (resolves T239136996).
Migrate deprecated top-level onBrokenMarkdownLinks to markdown.hooks.onBrokenMarkdownLinks
for Docusaurus v4 compatibility.

Author: saitcakmak

website/docusaurus.config.js

@@ -29,7 +29,11 @@ module.exports={
     "wrapPagesHTML": true
   },
   "onBrokenLinks": "throw",
-  "onBrokenMarkdownLinks": "warn",
+  markdown: {
+    hooks: {
+      onBrokenMarkdownLinks: "warn",
+    },
+  },
   "presets": [
     [
       "@docusaurus/preset-classic",

website/package.json

@@ -14,11 +14,10 @@
     "docusaurus": "docusaurus"
   },
   "devDependencies": {},
-  "//": "TODO: T239136996 Unpin Docusaurus canary after 3.8.2 or 3.9 is released",
   "dependencies": {
-    "@docusaurus/core": "3.8.1-canary-6401",
-    "@docusaurus/plugin-client-redirects": "3.8.1-canary-6401",
-    "@docusaurus/preset-classic": "3.8.1-canary-6401",
+    "@docusaurus/core": "^3.9.0",
+    "@docusaurus/plugin-client-redirects": "^3.9.0",
+    "@docusaurus/preset-classic": "^3.9.0",
     "clsx": "^1.1.1",
     "plotly.js": "^2.8.1",
     "react": "^18.3.1",