feat: show plaid link flow error

[sarahraines]

Description

This PR shows an error when Plaid is unable to link a bank rather than failing silently.

As an error state In the LinkAccounts component

As a dismissable modal in the LinkedAccounts component

[greptile-apps]

Greptile Summary

This PR implements comprehensive error handling for Plaid bank linking failures by introducing a new error state management system. The changes add a PlaidLinkErrorStoreProvider that uses Zustand to track Plaid link errors globally across the application.

The implementation integrates error detection in the useLinkedAccounts hook by adding an onEvent callback that listens for Plaid's ERROR events and records them in the store. When errors occur, users see different UI presentations depending on context: an alternate error state in the LinkAccounts onboarding component (via early return in LinkAccountsLinkStep) and a dismissable modal in the regular LinkedAccounts component.

The error UI provides two clear actions - "Link another bank" to retry the connection process, or "Complete" to proceed without linking additional accounts. The error state is automatically dismissed when a successful link occurs or when manually dismissed by the user.

The changes also include visual styling updates to the DataState component's error state, using proper design system error colors instead of transparent backgrounds, and responsive CSS for the error modal that stacks buttons vertically on smaller screens.

Confidence score: 4/5

• This PR is generally safe to merge with well-structured error handling that improves user experience
• The score reflects minor concerns about error event detection specificity and potential edge cases in async operations
• Files that need more attention: useLinkedAccounts.ts for the event handling logic and PlaidLinkErrorModal.tsx for the modal state management

_{9 files reviewed, 3 comments}

_{Edit Code Review Bot Settings | Greptile}

[doneel]

Where does this number come from? Asking to see if it's a repeatable constant we should re-use as a var.

[doneel]

I think this is inconsequential, but why should this PlaidLinkError component be nested under LinkedAccounts? We're reusing it for multiple other components.