Add sample CPA package with synthetic data

Add Cowork install instructions to README

Add 10 real-usage improvements from full tax return walkthrough

Remove personal data: purge design doc, genericize example addresses

Add update check to preamble (curl VERSION from GitHub)

Rewrite SKILL.md to XML structure, add prior return import and MCP detection

Add VERSION file and CHANGELOG for release tracking

Rewrite README with clear install steps and workflow diagram

Add CA + CT state guides, update all tax data for 2025

Initial scaffold: tax-prep Claude Code skill