Polish the release README with an animated demo

[ZILECAO]

Summary

• add a self-contained animated SVG showing the real AgentFormation browser-terminal experience
• embed the demo near the top of the README
• keep all example identity and workspace data generic, with no scripts or outside assets

Validation

• ./scripts/check.sh — passed: formatting, lint, types, 48 tests, production build, ShellCheck, and CloudFormation validation
• Gitleaks v8.30.1 — passed against the full Git history and release files
• xmllint --noout assets/agentformation-demo.svg — passed
• static 1200×720 render — visually reviewed
• live ECR image scan — 0 critical, high, medium, low, or undefined findings

This changes documentation only. It does not change or deploy the application, AWS resources, or the existing runtime. The repository remains private until an explicit publish step.