Create Supabase project with job queue migrations

[abrichr]

Set up the Supabase project and create database migrations for the job queue schema.

Acceptance criteria:

• Supabase project created and configured
• Job queue table with: id, repo_url, branch, status, created_at, started_at, completed_at, result
• Row-level security policies
• Migration files checked into the repo

[abrichr]

Implemented in PR #15 (merged to main as e7287b1).