Refactor frontend state management with Redux or Zustand

## Description
Current wallet and proposal state is scattered across component props and context.

## Acceptance Criteria
- Evaluate Redux, Zustand, or Recoil for state management.
- Migrate wallet and proposal state to centralized store.
- Simplify component prop drilling.

## Priority
Medium

## Estimated Effort
Large

## Dependencies
Issue #129

## Labels
enhancement