Create fork-friendly contribution and customization guides

[kai-linux]

Goal

Reduce friction for users who want to fork Agent OS, customize it, and contribute improvements back—currently 0 forks despite 2 stars.

Success Criteria

• CONTRIBUTING.md published with contributor expectations, commit conventions, code review process
• FORK_GUIDE.md created with customization patterns (agent routing, task dispatch, prompt configuration)
• Local development setup documented and tested end-to-end
• Fork metric tracked post-publication; target 3+ forks within 30 days

Constraints

• Target solo builder audience (assume Python/git familiarity, new to agent-os codebase)
• Customization guide focuses on high-leverage entry points only, not refactoring
• Do not modify existing code to be more fork-friendly—document current patterns as-is
• Keep documentation concise and example-driven

Outcome Checks

agent_success_rate, escalation_rate, task_completion_time, github_stars, github_stars_14d, github_forks, github_forks_14d, task_success_rate, completion_time