[Conformance] SEP-2484: Wire SEP traceability files into conformance test runner; surface per-SEP pass rates

Implements SEP-2484 for the MCP Spec 2026-07-28 release.

Tracked by umbrella #339.

Spec summary

Before any Standards Track SEP touching observable protocol behavior moves Accepted → Final, a tagged conformance scenario must be merged in the modelcontextprotocol/conformance repo with a sep-NNNN.yaml traceability file mapping each MUST/MUST NOT requirement.

PHP SDK changes

• No direct code change, but materially affects how the SDK tracks SEP adoption. The conformance suite at tests/Conformance/ (Docker-based) becomes the ground truth for "feature implemented."
• Use SEP traceability YAMLs to drive PHP coverage: each newly-Final SEP maps to a set of conformance scenarios that should pass against the PHP SDK before claiming support.
• Build on commits f12ea0a (conformance score calculation) and 3e45b1f (README badges): surface per-SEP pass rates next to the overall score.
• CI gate: when conformance suite adds a sep-NNNN.yaml, surface failures distinctly so adoption can be tracked SEP-by-SEP.

Related

• Umbrella #339
• Supports SDK Tier classification (SEP-1730)

tests/Conformance/ と Docker ベースの conformance runner から始め、既存のスコア計算と README バッジについてコミット f12ea0a と 3e45b1f を確認します。conformance repository の sep-NNNN.yaml ファイルから SEP ごとの結果を提供できる方法を追跡します。SEP ごとの合格率が表示され、新しい traceability ファイルが追加されたときに CI が失敗を区別できれば完了です。