docs: add agent rules for VAN CLI usage

[sunil-sadasivan]

Summary

• Add docs/agent-rules.md with operational rules for safe agentic van-cli / SDK usage
• Add top-level AGENTS.md with coding-agent repo context, build/test commands, CLI implementation conventions, and API safety guardrails
• Add top-level CLAUDE.md with Claude-focused project context and implementation reminders

Notes

The agent rules document follows patterns from comparable API-heavy CLIs:

• Salesforce CLI: document when to prefer bulk export over standard query paths
• AWS CLI/botocore: codify pagination/retry policy as reusable rules/metadata
• GitHub CLI: make pagination explicit and validate flag compatibility
• Stripe SDKs: require explicit limits for collecting auto-paginated data in memory

Test plan

• npm test