The proxy previously defaulted to bare "claude" command which fails in
macOS LaunchAgent where PATH is minimal. Now resolves the binary at
startup via: CLAUDE_BIN env → well-known paths → which fallback.
Fails fast with clear error if binary cannot be found.
Also enhances /health to report claudeBinary and claudeBinaryOk status.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
