feat: set AGENT=1 environment variable to identify AI agent execution

[swen128]

Summary

Sets the env var AGENT=1 at startup to identify when processes are run by an AI agent.

Context

Claude Code Implementation

Claude Code sets CLAUDECODE=1 environment variable for similar purposes. This is useful when you want to:

• Block AIs from touching certain sensitive scripts
• Enable stricter pre-commit hooks when code is being modified by AI
• Provide clear identification of AI-driven operations

Bun Test Integration

Bun's test runner already supports AI agent detection through the AGENT=1 environment variable:

• When AGENT=1 is detected, Bun shows concise, AI-friendly test reports
• This improves the AI's ability to parse and understand test results
• Documentation: https://bun.com/docs/cli/test#ai-agent-integration