Preserve separate responsive navigation surfaces

[chubes4]

Purpose

Keep independently authored desktop navigation and mobile details-disclosure navigation as separate responsive surfaces. This stacked PR depends on #1647.

Changes

• Keep captured disclosure navigation out of overlay-pair suppression.
• Avoid projecting navigation spacing onto the list-navigation class.
• Add a contract fixture for desktop navigation paired with a native mobile details disclosure.

Verification

• Navigation contract passed: canonical block style attributes, HTML-to-blocks, and format bridge scaffold.
• PHP lint passed for both production files.
• Frontend artifact compilation matched the authored desktop/mobile visibility variants and preserved the disclosure interaction.

Draft Gate

This is not a solved-site claim. Canonical fresh import verification has not yet run.

AI assistance: GPT-6 Astra through OpenCode was used for parallel implementation, review, and test orchestration.