Implements a service that uploads videos to YouTube via the Data API v3.
Resolves OAuth credentials from social-accounts, reads media files from
disk, and handles scheduled publishes by setting privacyStatus to private
with a publishAt timestamp. Includes 12 unit tests covering successful
uploads, scheduled publishing, credential/media validation, and API errors.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
