Auth moved to standalone controller outside Riverpod:
- New AuthController runs in main() before runApp()
- Handles callback, token exchange, and /auth/sync before app starts
- If auth not ready (redirecting), app doesn't start at all
- AuthProvider now just loads stored tokens (no async OIDC logic)
- Fixes "Cannot use Ref after disposed" errors
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
