[demolaf]

• Related to Customizable SwiftUI auth UI: content slots, per-screen state, and theming #1400

Adds DefaultAuthPickerContent(authMethodPicker:) so apps can lay out the provider buttons themselves, with the same MFA, account-conflict and error handling as the default buttons. Stacked on #1403.

Changes

• The layout closure receives an AuthMethodPickerState: providers, select(_:), isEmailLinkEnabled and selectEmailLink(), so a custom layout can't silently drop email-link sign-in. Its public init lets apps preview layouts with stub actions.
• AuthService gains registeredProviders and triggerSignIn(for:). The new opt-in AuthProviderAction covers providers with no credential and takes precedence when adopted; PhoneAuthProviderAuthUI adopts it.
• select(_:) reports an error for a provider that is neither credential-based nor AuthProviderAction, instead of doing nothing.
• The 14% horizontal inset moves into DefaultAuthMethodPicker, so custom layouts aren't padded. The default screen is pixel-identical to main.

API Usage

AuthPickerView { authenticatedApp }
  .pickerContent {
    DefaultAuthPickerContent { state in
      ForEach(state.providers, id: \.id) { provider in
        Button(provider.displayName) { state.select(provider) }
      }
      if state.isEmailLinkEnabled {
        Button("Email link", action: state.selectEmailLink)
      }
    }
  }

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Maintainer note: Fixes internal CPRN-517

[gemini-code-assist]

Code Review

This pull request introduces the AuthProviderAction protocol and updates AuthService to support programmatic sign-in for custom providers. It also refactors DefaultAuthPickerContent to allow custom layouts for provider buttons via AuthMethodPickerState and adds comprehensive unit tests. The review feedback suggests improving code readability and efficiency by avoiding unidiomatic try await .success(...) syntax and removing redundant VStack wrappers in SwiftUI views.