docs: record required framework check

[CircleQMinh]

Summary

• record that Validate framework candidate is required on main
• document strict/up-to-date branch protection with no review requirement
• advance the SEO handoff to the pre-cutover route-matrix gate

Why

Four stable framework candidate runs completed in 30-32 seconds, so the
previously advisory validation check has been promoted to a required check.

Validation

• live branch protection read back with strict status checks enabled
• exact required context: Validate framework candidate
• administrator bypass retained
• documentation diff check passed