Add Plasmate Audit and Plasmate A11y - SOM-powered site analysis

[dbhurley]

Plasmate Audit / Plasmate A11y

• plasmate-audit - SEO and content auditing powered by the Plasmate browser engine. 10x faster than Chrome-based auditors.
• plasmate-a11y - WCAG accessibility auditing via Semantic Object Model. 7 rules, CLI + Python API.

Both tools use Plasmate's SOM output instead of raw DOM, making analysis significantly faster and more token-efficient for AI-assisted workflows.

License: Apache 2.0
Language: Python + Rust