Improve Docusaurus accessibility and evidence #1637

Description

Improve Docusaurus accessibility behavior and make browser evidence exact, fail-closed, and reproducible. Cover mobile navigation focus, search semantics, target sizing, adaptive rendering, contrast inventory, generated route discovery, and automated NVDA execution configuration.

Acceptance Criteria

• Mobile navigation traps focus while open, marks background content inert, closes on Escape, and restores focus.
• Search controls meet target-size requirements and preserve keyboard focus and announcement behavior.
• Browser evidence covers deployed routes, adaptive states, focus geometry, Mermaid rendering, and exact method cells.
• Contrast collection closes a deterministic signature inventory and separates semantic route verdicts from qualified contrast review.
• Source and route discovery share one parser and fail on malformed or ambiguous metadata.
• The screen-reader binding and runtime configuration resolve all authored cases and support explicit isolated NVDA execution.

Related

• Evidence source: comprehensive accessibility review
• Scope: Docusaurus product behavior and browser evidence