Deduplicate progressive rendering pattern between playbook and mechanical skill

[jerelvelarde]

Priority: P2 | Source: PR #21 self-review (F5)

Problem

The progressive rendering / updateState → render() pattern appears in both master-agent-playbook.txt and mechanical-illustration-skill.txt with nearly identical code examples.

Suggested Fix

Remove the "Interactive Control Binding" section from mechanical-illustration-skill.txt and add a cross-reference: "See the Progressive Rendering architecture in master-agent-playbook.txt."