test: trigger api-docs workflow (do not merge)

[twishabansal]

Do not merge / do not review. Throwaway PR to exercise the api-docs.yml
deploy workflow from #690 on real runners.

Temporarily adds a pull_request: trigger to .github/workflows/api-docs.yml
(the only change). The workflow otherwise has no PR trigger, so this is the
only way to run it pre-merge.

Expected on this PR run:

• Resolver hits the default case (GITHUB_REF = refs/pull/N/merge) → builds
  core + adk + langchain + llamaindex as dev.
• Root-page step is skipped (not a tag).
• Deploy step pushes the built dev docs to the gh-pages branch
  (keep_files: true, so existing content is preserved).

Revert the temp trigger and close this PR once the run is confirmed.

[twishabansal]

Real-runner test passed: workflow built core/adk/langchain/llamaindex as dev, skipped the root step (not a tag), and deployed to gh-pages. All four //dev/ pages plus latest/ + releases.releases are live at py.mcp-toolbox.dev (200, real content). Closing the throwaway PR; the PR #690 branch never carried the temp trigger.