## Summary
- Store SSO connections (Google, Microsoft, OIDC, SAML) as connected
accounts in the core schema during sign-in/sign-up, gated behind the
`IS_CONNECTED_ACCOUNT_MIGRATED` feature flag
- Add `OIDC` and `SAML` to `ConnectedAccountProvider` enum with
exhaustive switch handling across frontend and backend
- Add `IS_CONNECTED_ACCOUNT_MIGRATED` to `DEFAULT_FEATURE_FLAGS` for new
workspaces, with a fallback check so SSO accounts are created even
before workspace activation
- Always upsert connected accounts to both workspace and core schemas
during messaging OAuth flow, fixing FK constraint violations when
SSO-only accounts exist only in core
- Create message/calendar channels when they don't exist regardless of
new vs reconnect flow
- Filter settings accounts list to only show accounts that have message
or calendar channels
## Test plan
- [ ] Sign up with Google SSO → verify connected account is created in
core schema
- [ ] Connect messaging (Google APIs) after SSO sign-up → verify no FK
errors, channels created, configuration page renders correctly
- [ ] Reconnect an existing messaging account → verify tokens updated,
sync resets triggered
- [ ] Sign in with OIDC/SAML SSO → verify connected account created with
oidcTokenClaims
- [ ] Verify settings accounts page only shows accounts with channels
(SSO-only accounts hidden)
- [ ] Verify typecheck, lint, and unit tests pass
