Preflight PHP wasm runtime assets

[chubes4]

Summary

• Add a PHP wasm runtime asset preflight before WordPress Playground runtime creation so missing/corrupt selected wasm files fail before Playground boot.
• Record selected PHP wasm package/version/mode/loader/wasm path/size/hash in runtime metadata and lifecycle events for successful runs.
• Surface recipe-run failures as structured PHP wasm diagnostics with a concrete dependency reinstall/cache repair hint.

Tests

• npm run build
• npm run php-wasm-preflight-smoke
• npm run boot-preview-smoke
• npm run recipe-playground-boot-failure-smoke

Caveats

• The preflight follows the currently selected Node runtime package and selected JSPI/asyncify mode. If upstream Playground changes its package layout or loader filename conventions, this intentionally fails early with a loader/wasm-path diagnostic rather than booting with unverifiable assets.

Closes #623.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (gpt-5.5)
• Used for: Drafted the PHP wasm preflight implementation, smoke coverage, verification steps, and PR description. Chris remains responsible for review and merge decisions.