test: trigger backfill workflow (do not merge)

[twishabansal]

Do not merge / do not review. Throwaway PR to exercise api-docs-backfill.yml
pre-merge via a temp pull_request trigger (falls back to llamaindex/v0.7.0).

api-docs-backfill.yml is otherwise workflow_dispatch-only, so this is the
only way to run it pre-merge. On a pull_request event there are no dispatch
inputs, so the steps fall back to llamaindex/v0.7.0 via inputs.x || 'default',
and the checkout ref uses github.head_ref so the run sees docs-site/+scripts/
(not yet on main).

Expected on this PR run:

• Resolves llamaindex → packages/toolbox-llamaindex, overlays the
  toolbox-llamaindex-v0.7.0 tag's src/ onto main.
• Builds /llamaindex/v0.7.0/ docs.
• Opens a backfill/llamaindex-v0.7.0 PR against gh-pages (additive; not
  auto-merged).

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