Extract navigation toggle suppression policy

[chubes4]

Summary

• Move hamburger/nav-toggle suppression policy out of HtmlTransformer into Support\NavigationToggleSuppressionTrait.
• Keep the moved method bodies behavior-preserving while reducing HtmlTransformer size and giving generic nav-toggle policy clear ownership.
• Leave fixture outputs unchanged.

Testing

• composer test (from php-transformer)

AI assistance

• AI assistance: Yes
• Tool(s): OpenAI GPT-5.5 via OpenCode
• Used for: Identified a non-overlapping PHP transformer refactor after trunk refresh, moved the navigation toggle suppression policy, ran tests, and drafted this PR description.