Support importing author, collection, and post data from a pull request webhook

Note: See the sub-issues for actual tasks. The description below is vague notes / future planning beyond the scope of this issue.

When someone creates a pull request to the content repository (to be created / split from the Astro codebase in the future), hoof should:

• Look up the author of the pull request
• Determine if they have an account in the CMS (TBD: how?)
  • If not, create a profile/user record in the DB
    • TBD: should they be prompted to complete oauth to create an account via PR comment?
• Obtain the forked repo/branch from the PR webhook event
• Import the post under the author's profile as a draft
  • TBD: We need the frontend to expose a no-index page for viewing a draft post from the API
• Send a build status back to the PR to indicate if the import was successful

If the same post is later sent via a push webhook from main, the post should be marked as published with the webhook date as the timestamp.

No files or tests are named, and the issue says the actual tasks belong in sub-issues. Start by finding those sub-issues and the pull-request and push webhook entry points, then map the CMS/database import and PR status flows. Done criteria are not yet scoped beyond author lookup, draft import, build status, and later publication.