Fix browser recipe artifact handling

[chubes4]

Summary

• Keep preview holds only for successful recipe runs so failed browser runs release immediately and preserve diagnostics.
• Add a WP Codebox runtime activation hook after extra plugin activation for consumers that need to finish runtime registration after all plugins are active.
• Preserve browser-generated website artifact bundles and use inline package URLs for Playground-installed plugin packages.

Testing

• npm run build
• php tests/smoke-wordpress-plugin.php
• node scripts/browser-runtime-operation-smoke.ts
• Live Studio Web headless eval was rerun against this branch; it progressed beyond the missing agents/chat handler once paired with the Studio Web runtime-policy fix, then exposed the next blocker: the sandbox agent bundle is not installed.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (openai/gpt-5.5)
• Used for: Drafted and tested the runtime fixes; Chris directed the debugging path and reviewed the resulting behavior.