Add patch exploit chain grouping gates

[malb200710-dev]

Summary

• Adds exploit-chain and blast-radius grouping to patch prioritization.
• Requires chain role, shared boundary, prerequisites, blast radius, tier adjustment, and patch grouping evidence.
• Adds an Exploit Chain Patch Groups output table and a pitfall about isolated CVE prioritization.
• Links implementation to review issue [REVIEW] patch-prioritization: add exploit-chain blast-radius grouping gates #2241.

Validation

• Confirmed markdown code fences are balanced.
• Checked the new version, exploit-chain step, output table, and changelog are present.

Bounty request: Improver Moderate ($100) if accepted. I can provide payment details if accepted.