feat: add agentready-dev Claude agent specification (#44)

- Create comprehensive agent specification for AgentReady development
- Includes architecture overview, assessment workflow, and design patterns
- Documents all 15 stub assessors and reference implementations
- Provides constitutional principles and anti-patterns to avoid
- Includes common tasks, debugging strategies, and success criteria

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Jeremy Eder <jeremyeder@users.noreply.github.com>

Author: jeremyeder