chore(deps): simplify dependabot config to root only

Yarn workspaces hoists all dependencies to the root yarn.lock, so
Dependabot only needs to scan from / — it will pick up package.json
files across all workspace packages automatically.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sserrata

.github/dependabot.yml

@@ -4,11 +4,3 @@ updates:
     directory: /
     schedule:
       interval: daily
-  - package-ecosystem: npm
-    directory: /packages/docusaurus-plugin-openapi-docs
-    schedule:
-      interval: daily
-  - package-ecosystem: npm
-    directory: /packages/docusaurus-theme-openapi-docs
-    schedule:
-      interval: daily