ci: auto-request Copilot review on PR open

[fazleelahhee]

Summary

• Adds .github/workflows/copilot-review.yml that runs on pull_request: opened and ready_for_review, requesting review from Copilot (copilot-swe-agent, bot ID BOT_kgDOC9w8XQ) via the GraphQL requestReviews mutation.
• Skips draft PRs; uses union: true so it never displaces existing reviewers.
• Branch protection on main was updated separately: required_approving_review_count: 0, require_code_owner_reviews: false. The 10 CI status checks, admin enforcement, and conversation-resolution requirement remain in place.

Test plan

• On opening this PR, the Request Copilot review workflow runs and Copilot is added as a reviewer.
• Any collaborator can merge once CI is green, with no human approval required.

[fazleelahhee]

Closing — Copilot review integration not needed.