Improve raw HTML block conversion

[chubes4]

Summary

• Fix standalone anchor paragraph serialization so anchor markup stays in saved HTML without duplicating raw HTML into paragraph delimiter attributes.
• Treat legacy center/font markup as traversable visible content so FrontPage-era HTML produces non-empty block markup.
• Preserve static script metadata separately from runtime script fallbacks and classify runtime script fallback details.

Matrix evidence

Combined local raw HTML matrix with SSI integration + Blocks Engine integration:

• 41/41 imports succeeded
• hard failures: 1 -> 0
• fallbacks: 45 -> 15
• core/html blocks: 0 -> 0
• freeform blocks: 0 -> 0
• invalid block documents after SSI semantic validation: 202 -> 0
• summary: /var/folders/lr/c_cmmt7s0592m4njz99v5yb40000gn/T/opencode/raw-html-combined-matrix-v2/summary.json

Testing

• composer test from php-transformer/
• Combined local raw HTML matrix via SSI worktree with this transformer package preloaded

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 via OpenCode
• Used for: Diagnosis, implementation, fanout integration, and local verification.