Implements `core login CODE` — exchanges a 6-digit pairing code generated
at app.lthn.ai/device for an AgentApiKey, persisted to ~/.claude/brain.key.
Pairing code is the proof, so the POST is unauthenticated.
- auth.go: AuthLoginInput/Output DTOs + handleAuthLogin handler
- commands_platform.go: login / auth/login / agentic:login CLI commands
with cmdAuthLogin persisting the returned key
- prep.go: registered agentic.auth.login / agent.auth.login actions
- auth_test.go / commands_platform_test.go / prep_test.go: Good/Bad/Ugly
triads per repo convention, including key persistence verification
Co-Authored-By: Virgil <virgil@lethean.io>
