AD-1001: Add basic agent workspace example

[alph-cmky]

Summary

• Add a basic local-first example workspace under examples/basic-agent-workspace.
• Add a read-only code reviewer agent definition.
• Add a review workflow with Start, Agent, Human Approval, and End nodes.
• Document how to inspect and verify the demo locally.
• Update the AD-1001 backlog checklist.

Testing

• node -e "const fs=require('fs'); JSON.parse(fs.readFileSync('examples/basic-agent-workspace/agents/reviewer.json','utf8')); JSON.parse(fs.readFileSync('examples/basic-agent-workspace/workflows/review-flow.json','utf8')); console.log('example JSON ok')"
• pnpm lint && pnpm format && pnpm typecheck && pnpm test && pnpm build

Stacked on #48.

Closes #24