Add agent CLI script audit demo content

[rogerchappel]

Summary

• adds an agent CLI fixture for ScriptAudit demos
• adds config-backed tutorial and video brief grounded in the scan command
• links the walkthrough from the README

Verification

• npm test
• node dist/cli.js scan examples/fixtures/agent-cli --config ../../agent-cli-audit.config.json --out /tmp/scriptaudit-agent-cli.md
• node dist/cli.js scan examples/fixtures/agent-cli --config ../../agent-cli-audit.config.json --format json >/tmp/scriptaudit-agent-cli.json