chore(skills): check architecture and code placement in review-branch

What

Adds an Architecture and code placement check to Phase 1 (Correctness) of /review-branch. It reads docs/dev/architecture.md and flags new business logic placed inline in a handler where it belongs in a service or model layer (an anemic domain model), matching the format packages' convention of extracting pure domain logic into HTTP-free files (maven/parse.go, npm/validate.go, oci/digest.go).

Why

The skill loaded go-style.md and conventions.md but never architecture.md, so layering and anemic-model findings were invisible to the automated review and only surfaced in human review — as happened on !752 (merged), where the maven sidecar handler carried its validation and column selection inline.

The check is deliberately calibrated to DECISION / OBSERVATION, not BLOCKING, and explicitly does not flag code that merely matches the existing pattern of its package. The end-state handler-versus-service-layer split is still under discussion (#233), so this surfaces newly-introduced misplacement for a human decision without blanket-blocking the current handler-orchestration pattern.

Type

chore(skills) — project tooling. No product code changes; exempt from the related-issue guardrail.