WCAG Accessibility Agent v1.0

feat: initial release — WCAG 2.1 accessibility agent

- SKILL.md + references/: portable WCAG 2.1 knowledge base grounded in W3C WAI
- agent.py: agentic CLI with tool-use loop (fetch, read, write, export)
- Five operation modes: analysis, audit, evaluation, correction, handoff
- Three discipline levels: UX, UI, development
- PDF export via PyMuPDF, DOCX handoff via python-docx
- Installable skill file for Claude.ai (wcag-accessibility.skill)
- Covers 78 WCAG 2.1 success criteria across levels A, AA and AAA

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>