Add logveil tutorial and social hooks

[rogerchappel]

Summary

• add a fixture-backed tutorial for sanitizing an agent session
• link the tutorial from the README quick start
• add grounded social hooks and a demo clip outline

Verification

• npm install -> added 9 packages, found 0 vulnerabilities
• npm run build -> passed
• node dist/cli.js redact examples/agent-session.log --out repro-safe.md --json-out redaction-evidence.json -> wrote both files
• test -s repro-safe.md and test -s redaction-evidence.json -> passed
• node dist/cli.js audit examples/agent-session.log --format json --fail-on secret -> exited 2 with 2 secret findings, as expected
• npm run smoke -> passed