Add generic routing materialization plan rows

[chubes4]

Summary

• Add product-neutral materialization plan rows for routes, navigation links, and menus in php-transformer.
• Derive route candidates from compiled pages and navigation/menu candidates from compiled navigation markup.
• Cover the new rows in contract and parity fixtures, and document the result-envelope surface.

Testing

• composer test
• git diff --check -- php-transformer

AI assistance

• AI assistance: Yes
• Tool(s): openai/gpt-5.5 + OpenCode
• Used for: Implementing php-transformer materialization plan changes, tests, docs, and PR preparation.