Reconcile language-neutral verifier cases with current integrity bindings

[aruintelligence]

Reconciles the useful core of PR #68 against current main without regressing newer verifier-contract work.

Changes:

• adds a language-neutral exact verifier case corpus;
• keeps the existing public case descriptions for compatibility while pointing to the authoritative case file;
• makes the conformance harness consume the data-defined cases;
• preserves exact challenge and witness-vector SHA-256 bindings and adds a case-corpus SHA-256 binding;
• includes the case corpus in the reference-code-free external verifier kit;
• extends tests to prove the harness consumes data rather than hard-coded tamper objects.

Evidence boundary: a PASS remains project-defined black-box interoperability evidence. It is not certification or proof of implementation independence.

Supersedes the implementation intent of PR #68 while retaining newer work already present on main.

[aruintelligence]

Superseded by #170. The Snapshot 3 verifier-contract work was replayed as one clean commit on top of current main after the licensing, real-screen evidence, and release-discipline merges landed. This avoids carrying a stale base forward while preserving the vetted language-neutral case corpus, explicit Snapshot 2 → Snapshot 3 migration, catalog/lineage updates, hash bindings, and current-snapshot-aware tests.