CLAUDE.md, GEMINI.md, AGENTS.md, and copilot-instructions.md were being
silently overwritten on every `medusa init --ide` call. This destroyed
user customizations without warning.

Now checks if files exist before writing. Existing files are preserved.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>