Add deterministic CI state classifier for GitHub MCP server PR triage

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.