Fix/shared settings state

[d3v-active]

This PR addresses four distinct issues raised for the FlowFi frontend:

1. useSettings Shared State Refactor

• Issue: useSettings hook previously held per-instance state without a shared store or storage listener, meaning settings changes did not propagate across components or tabs.
• Fix: Re-implemented the useSettings hook using a shared source of truth paired with a subscriber pattern.
• Additions: Added a window storage event listener to automatically sync settings across different browser tabs.
• Tests: Included unit tests asserting multiple consumers correctly reflect changes simultaneously without remounting, and tests verifying cross-tab synchronization.

closes #854

2. useIncomingStreams Unit Tests

• Issue: Missing critical behavior tests for useIncomingStreams and useWithdrawIncomingStream hooks.
• Fix: Created comprehensive unit tests in useIncomingStreams.test.ts validating query key shapes and hook execution conditions.
• Tests Added:
  • Validated that useIncomingStreams stays reliably disabled (prevents fetches) when publicKey is null or undefined.
  • Verified useWithdrawIncomingStream correctly rejects immediately when the user session is missing.
  • Mocked dependencies using a QueryClientProvider wrapper to securely verify onSuccess query invalidation behavior.

closes #855

3. TokenStep Accessibility Improvements

• Issue: Stream token cards conveyed selection solely visually via borders and colors, breaking expectations for assistive technology users.
• Fix: Applied proper semantic ARIA attributes.
  • Exposed individual item selected states via role="radio" and aria-checked bindings on the token buttons.
  • Grouped token buttons securely inside a role="radiogroup" wrapper with an accessible group label (aria-labelledby).
  • Correlated validation errors back to the group context using aria-describedby.

closes #859

4. Dashboard Data Fetching Optimization (React Query Migration)

• Issue: Dashboard re-fetched the full snapshot manually per SSE event with no debounce, which caused request storms and out-of-order state modifications.
• Fix: Fully migrated DashboardSnapshot data fetching to useQuery utilizing @tanstack/react-query.
• Enhancements:
  • Bound an AbortSignal all the way down to the API calls inside fetchStreams to correctly cancel trailing pending requests when an SSE invalidates the cache again.
  • Capitalized on queryClient.invalidateQueries automatically coalescing and deduplicating redundant sequential SSE-triggered invalidations, natively preventing request storms.
  • Refactored local optimistic state modifiers to properly utilize queryClient.setQueryData replacing standard React component state.

closes #857