chore(ci): automate vendored OpenAPI spec updates via scheduled workflow

[marythought]

Problem

The vendored OpenAPI specs in specs/ regularly fall out of date with upstream opentdf/platform. This blocks contributors (especially external ones) whose PRs fail the check-vendored-yaml build step even though they didn't touch any specs. Maintainers have to manually run npm run update-vendored-yaml and commit the result.

Proposed solution

Add a scheduled GitHub Actions workflow (update-vendored-specs.yaml) that:

1. Runs daily on a cron schedule (+ manual workflow_dispatch)
2. Runs npm run update-vendored-yaml
3. If specs changed, opens a PR on the chore/update-vendored-specs branch (or force-pushes to an existing one)
4. PR auto-updates on subsequent runs until merged

Modeled after the update-protos workflow in opentdf/web-sdk.

This keeps specs fresh so contributors don't hit stale-spec build failures on their PRs.