fix(opy): converge source failure frontiers

[e54-bot]

Summary

• Resolve the remaining source-frontier mismatches identified by Resolve residual source failure-frontier mismatches after #162 #167.
• Add source constant declarations, ordinary @name annotations, multiline comprehension handling, JSONC settings expressions/comments, and the required catalog-backed receiver members.
• Preserve semantic diagnostics and provenance so the 6v6 fixture reaches unknown-member and issue-29 reaches duplicate-rule-name, matching the pinned oracle categories.
• Update conformance expectations, focused regression tests, manifest probes, and language-support documentation.

Validation

• cargo fmt --all -- --check
• cargo clippy --locked --workspace --all-targets --all-features -- -D warnings
• cargo test --locked --workspace --all-targets --all-features
• 35 compatibility tests and 43 manifest probes
• Full conformance: 46 match / 15 divergence / 2 inconclusive; both Resolve residual source failure-frontier mismatches after #162 #167 target fixtures match their pinned semantic frontiers.

Fixes #167

[Teakowa]

Please address the inline finding.

[Teakowa]

Major — This fallback classifies an unquoted OPY settings expression as SettingsNode::String. That is not just an opaque carrier: the compiler maps HIR String directly to workshop_rs::settings::SettingsNode::String, so a valid expression-valued setting that reaches backend lowering is emitted as a literal string instead of preserving/evaluating the expression. workshop-rs already distinguishes raw settings specifically to avoid fabricating a type. Preserve this as an explicit non-literal/unsupported expression (and fail lowering if necessary) rather than representing it as String.

[Teakowa]

LGTM