docs: add DO VPS verification guidance for coding agents

[benvinegar]

Summary

• add repo-wide guidance in AGENTS.md encouraging real Linux VPS verification when a DigitalOcean key is available
• clarify that DO_API_KEY should be treated as an alias for canonical DO_API_TOKEN
• recommend Arch Linux as the first-pass lightweight verification target
• point agents to existing helpers (bin/ci/droplet.sh, bin/ci/setup-arch.sh) and require cleanup of temporary cloud resources
• add CODEX.md as a symlink to AGENTS.md so coding-agent entrypoints share the same guidance

Notes

• docs-only change

[greptile-apps]

Greptile Summary

This PR adds comprehensive DigitalOcean VPS verification guidance to AGENTS.md and creates CODEX.md as a symlink to ensure coding agents have consistent documentation access. The new section provides clear instructions for real Linux testing, correctly references existing helper scripts (bin/ci/droplet.sh, bin/ci/setup-arch.sh), clarifies the DO_API_TOKEN canonical variable naming, and includes important security warnings about credential handling and resource cleanup.

Confidence Score: 5/5

• This PR is safe to merge with no risk
• Documentation-only change with accurate references to existing scripts and workflows, clear security guidance, and no code modifications
• No files require special attention

Important Files Changed

Filename	Overview
AGENTS.md	Added clear DigitalOcean VPS verification guidance with proper security warnings and references to existing helper scripts
CODEX.md	Created as symlink to AGENTS.md to ensure consistent agent guidance across entrypoints

_{Last reviewed commit: c6ce1f4}