Classify commerce runtime controls

[chubes4]

Summary

• Adds provider-aware PHP transformer diagnostics for form and commerce fallback lanes without adding SSI/provider-specific code to Blocks Engine.
• Classifies data-entry/static forms with controls as provider-materializable form targets, carrying materialization_target metadata for a downstream form provider instead of implying SSI lacks a form provider.
• Separates commerce product materialization from cart runtime behavior: product grids carry structured product metadata for a shop/product provider, while quantity/add-to-cart controls stay a dedicated cart-runtime diagnostic.
• Carries materialization targets, product rows/counts, and provider-role hints through conversion-report diagnostics so SSI can consume the structured intent.

Verification

• composer test from php-transformer/
• php tests/parity/run.php from php-transformer/
• php tests/smoke-form-materializer.php from Static Site Importer
• php tests/smoke-product-materializer.php from Static Site Importer

Notes

• PHP transformer only. No packages/blocks-engine/** changes.
• Static Site Importer already has generic pluggable providers: form => jetpack via Static_Site_Importer_Form_Seeder, and shop => woocommerce via the Woo product seeder/materializer. This PR now reflects that architecture.
• Remaining gaps are cart/control runtime binding and non-mappable forms, not absence of SSI form/product providers.

AI assistance

• AI assistance: Yes
• Tool(s): GPT-5.5 via OpenCode
• Used for: Inspected SSI provider architecture, corrected PHP transformer diagnostics/tests, updated the PR description, and ran verification.