chore: upgrade Redux stack (RTK 2.x, react-redux 9.x, redux 5.x)

[hb2708]

Summary

Upgrade the Redux ecosystem to the latest major versions. The project currently uses RTK 1.x which is significantly behind the modern Redux patterns introduced in RTK 2.x.

Current → Target

Package	Current	Latest
@reduxjs/toolkit	1.8.6	2.x
react-redux	8.0.4	9.x
redux	4.2.0	5.x
redux-thunk	2.4.1	3.x (bundled in RTK 2.x)

Why Upgrade

• RTK 2.x introduces improved TypeScript support, better defaults, and the new listenerMiddleware
• react-redux 9.x has performance improvements and drops legacy context usage
• Redux 5.x is a TypeScript rewrite with improved types
• redux-thunk is bundled in RTK 2.x — no longer needed as a separate dependency

Migration Steps

1. Upgrade all packages together — these are tightly coupled:

   yarn add @reduxjs/toolkit@latest react-redux@latest redux@latest
   yarn remove redux-thunk

2. Review configureStore usage — RTK 2.x changes some defaults:
   • redux-thunk is included automatically — remove manual middleware addition
   • serializableCheck and immutabilityCheck are on by default
3. Update createSlice usage — check for deprecated patterns:
   • createSlice reducers now support a builder callback (preferred)
   • Check any extraReducers using the map object notation → switch to builder
4. Fix TypeScript types — RTK 2.x exports improved types:
   • RootState and AppDispatch inference should still work but verify
   • useSelector and useDispatch hooks may need typed versions
5. Run tests — yarn ci to ensure all 435 tests still pass

Files Likely Affected

• app/ducks/ — all Redux slices and store configuration
• Any component using useSelector/useDispatch
• Store setup file (likely configureStore call)

References

• RTK 2.0 Migration Guide
• react-redux v9 Release Notes
• Redux 5.0 Release Notes