Implements `flynn gmail-auth` to complete the OAuth2 flow that
GmailWatcher references but was never built. Supports local callback
server (default) and --manual paste mode. Adds Gmail health check
to `flynn doctor`.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
- Extract createClientFromConfig() to dispatch on provider field instead
of hardcoding all tiers as AnthropicClient
- Add fallback/fallbackReason metadata to ChatResponse and ChatStreamEvent
so callers know when a fallback model was used
- Enhance doctor check to report full model stack and warn on missing
API keys for cloud providers
- Log fallback warnings in NativeAgent and display them in TUI
- Support tier names and local_providers entries in fallback_chain
- Add 8 tests for createClientFromConfig covering all provider types
William Valentin