Description

Copied from #2013 as new feature: On startup, the extension should check process.env.ANTHROPIC_API_KEY. If the key is set and the API Provider is set to Claude Code, the extension must show a prominent VS Code warning notification. The warning should state: "An ANTHROPIC_API_KEY environment variable was detected. This may conflict with your subscription login and cause errors. Please unset it to ensure your Claude Max/Pro plan is used."