build(deps): bump documents.js to 4.0.20

Triggered instantly via repository_dispatch when documents.js published its own release,
rather than waiting for the next scheduled Dependabot scan.

Author: github-actions[bot]

package.json

@@ -89,7 +89,7 @@
   "dependencies": {
     "commander": "^15.0.0",
     "document-outline.js": "^1.0.0",
-    "documents.js": "^3.1.5",
+    "documents.js": "^4.0.20",
     "ink": "^7.1.1",
     "ink-text-input": "^6.0.0",
     "react": "^19.2.8"