feat(conformance): define Workshop evidence contract

[Teakowa]

Summary

Implements #18 by adding the canonical workshop_rs::conformance public contract.

• Adds namespace-qualified, locale-independent FeatureId values derived from canonical catalog identities or workshop-rs-owned namespaces.
• Adds machine-readable result states: matched, unsupported, known-gap, unexpected-regression, and inconclusive.
• Separates executed fixture provenance from independent expectation provenance and records catalog, locale, implementation, and live-client metadata.
• Adds structured comparison artifacts/reason codes, SHA-256 validation, and a validated JSON entry point.
• Documents the public ownership and downstream-consumer boundary in ADR-0002.

Evidence and checks

The contract has focused positive/negative serialization and validation tests, including duplicate features, status/reason mismatch, missing live-client provenance, missing artifact digests, implementation metadata not serving as an oracle, and a format-valid mismatched catalog-digest regression.

ConformanceResult::validate_against requires the complete evidence.catalog == supplied Catalog::identity() before accepting catalog-backed feature identities.

• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace --all-targets
• cargo run -p workshop-rs --bin workshop-catalog-gen -- check
• git diff --check

This PR establishes the offline contract only. It does not claim census coverage, real-project evidence, or live-client captures; those are the dependent #19–#21 workflows.

[Teakowa]

Architect review\n\nIndependent Architect review identified four contract risks before dependent work: unscoped feature names, fixture/expectation provenance conflation, free-text-only result semantics, and raw JSON deserialization bypassing validation. Commit 0bf6917 addresses these by adding namespace-qualified identities (including domain-qualified enum members), separate fixture/expectation artifacts, structured comparison/reason codes with digest checks, and ConformanceResult::from_json validation. The review boundary remains explicit: this PR establishes the contract only; #19/#20/#21 must consume it without redefining it. No Architect approval is being claimed here; maintainer review remains required.

[Teakowa]

Fresh QA found an artifact-aliasing false-positive risk. Commit 68a4340 now rejects matched expected/observed artifacts that are identical to each other, the executed fixture, or the recorded implementation artifact, with a regression test. This was revalidated locally with focused conformance tests, clippy -D warnings, catalog check, and diff-check; full CI is required again at the new head.

[Teakowa]

QA follow-up addressed in commit 0e2ee3d: validate_against(Catalog) now rejects fabricated catalog and enum-member identities; comparison artifacts remain valid when non-materialized (optional SHA-256); ADR-0002 explicitly assigns execution of semantic/normalized comparison to the independent #19 gate. Local full workspace tests, clippy, catalog check, fmt, and diff-check pass. Awaiting fresh CI and QA review at this head.

[Teakowa]

Fresh QA blocker resolved in commit 9a1f753: expected artifacts are now also rejected when they alias the implementation artifact, while expected == expectation.artifact remains the valid independent-oracle relationship. Added regression coverage. Current local conformance tests/clippy/catalog check pass; awaiting CI and final independent QA.

[Teakowa]

Fresh independent QA — VERIFIED / PASS

Exact head reviewed: 58832ff74326ac438f121895d54d3c791b6c4dfd.

• ConformanceResult::validate_against requires exact evidence.catalog == catalog.identity().
• The format-valid mismatched-catalog digest regression rejects the wrong identity.
• Define the Workshop conformance result contract and stable feature identities #18 status/provenance/serialization and provider-neutral ownership boundaries are covered.
• Local fmt, Clippy, workspace/all-targets tests, catalog check, and diff check passed.
• Stable and Rust 1.85 CI passed on this exact head.
• Worktree is clean and HEAD matches the PR head.

The previous QA on 9a1f753 is superseded by this exact-head review. No findings. #18 is ready for maintainer merge review.