Fix editor presentation capture diagnostics and canvas selection

[chubes4]

Summary

• initialize WordPress style and script registries before reading block editor settings from CLI
• frame the internal presentation JSON payload so PHP diagnostics cannot corrupt transport
• preserve bounded PHP output when framing is missing or invalid
• select any visible non-iframed editor canvas instead of assuming the first match is visible

Closes #2437.

Verification

• npx tsx --test tests/browser-routed-command-security.test.ts
• npm run build
• Replayed the 15-saas solved-site recipe through WordPress 7.0.4. wordpress.editor-open captured all six expected presentation identities with complete coverage.

AI assistance

OpenAI GPT-5.6 Sol via OpenCode reproduced the released-package failure, traced the WordPress and browser readiness boundaries, implemented the focused repair, and ran the verification under human direction.