Support API key authentication for interactive mode on headless systems

Problem

On a headless Raspberry Pi (no browser, no GUI), it's impossible to authenticate Claude Code for interactive mode. The OAuth flow requires a browser, which isn't available.

What works: claude -p "prompt" works fine with ANTHROPIC_API_KEY env var set.

What doesn't work: claude (interactive mode) always shows the login screen and requires browser-based OAuth, ignoring the ANTHROPIC_API_KEY environment variable.

Attempted workarounds (all failed)

• Setting ANTHROPIC_API_KEY env var — ignored by interactive mode
• claude login --api-key — unknown option
• claude auth login --method api-key — unknown option
• apiKeyHelper in ~/.claude/settings.json — still shows login screen
• Text-based browser (lynx) — OAuth page requires JavaScript
• Device code flow (entering code on another machine) — hangs after entering code, never completes
• claude config set --global apiProvider anthropic — doesn't skip login

Expected behavior

When ANTHROPIC_API_KEY is set, claude interactive mode should use it directly without requiring browser-based OAuth — the same way claude -p already does.

Environment

• Claude Code v2.1.71
• Raspberry Pi 4 (4GB RAM), Debian ARM64
• Headless (SSH only, no display/browser)