Anthropic now blocks third-party apps from using Pro/Max subscription
quotas via direct API calls. This change makes the claude-code provider
(which delegates to the local claude CLI binary) the default path for
Anthropic subscription users — TOS-compliant because requests flow
through Anthropic's own infrastructure.
Changes:
- Enhanced readiness check to verify CLI auth status (not just binary)
- Startup migration: auto-switch anthropic → claude-code when CLI ready
- Error recovery: auto-switch on third-party 400 block error
- Onboarding: removed Anthropic from OAuth, added Claude CLI option
- Added claude-code to flat-rate providers (no dynamic routing benefit)
Closes#3772
