Add deterministic CI state classifier for GitHub MCP server PR triage

[davidahmann]

PR triage can misclassify missing or policy-gated checks, which delays correct action and creates unnecessary code churn.

Current behavior is insufficient because CI outcomes are manually interpreted and not emitted as a deterministic contract.

Why now: this server participates in cross-repo maintenance workflows that depend on normalized state semantics.

Claim-to-codepath map:

• CI workflow/status ingestion in .github/workflows and script tooling.
• Classification output consumed by e2e and maintenance paths.

Requested behavior: add deterministic state classification output and tests for failed, pending, no-checks, and policy-blocked scenarios.

Evidence Packet

• Commit under test: 16ff74a
• Runtime environment:
  • OS: Darwin 25.3.0 arm64
  • Python 3.14.0
  • go version go1.25.7 darwin/arm64
  • Node: v22.19.0
• Minimal repro:
  1. Follow the repo's current local validation/CI-triage path.
  2. Observe the behavior described above for this issue.
• Expected behavior: deterministic, documented behavior matching acceptance criteria below.
• Actual behavior: behavior can be inconsistent for the scenario described above.

Acceptance Criteria

• Implement the smallest code change that addresses the proven pain point.
• Add focused regression test coverage for the changed behavior.
• Ensure backward compatibility expectations are explicit in tests/docs.