fix(php-transformer): compact composed site plan views

[chubes4]

Breaking Contract

compact() accepts only the canonical blocks-engine/wordpress-site-plan-view/v1 view and produces compact v2. materialize() accepts only compact blocks-engine/wordpress-site-plan-view/v2 and reconstructs canonical v1. v1 serialized views are not accepted as persisted compact input.

Release Coordination

This breaking pre-1 Blocks Engine PHP Transformer contract should ship as a SemVer minor release. Static Site Importer PR #1578 consumes it directly. SSI's Composer pin remains intentionally unchanged here; its parent must supply the actual released BE version in a follow-up dependency edit. No release, deployment, version, or changelog change is included.

Evidence

• composer test passes, including package-install proof against this candidate.
• Contract coverage runs compile -> compact -> JSON persist/restore -> materialize and compares the exact canonical plan hash. It covers UTF-8, base64, binary bytes, tampering, v1 materialize rejection, and v2 compact rejection.
• Read-only Studio evidence: the static-artifact-import companion directory contains only documentation; uploads have no composed-result files. The only matching receipt is unrelated Brezzelo data containing canonical blocks-engine/wordpress-site-plan/v2 plans, not serialized views. No checkpoint or artifact-run was mutated, invalidated, or migrated.

AI Assistance

Implemented with openai/gpt-5.6-terra via OpenCode for contract correction, testing, and review.