feat(portal): add financing slice w/ optimistic updates + global 5xx …

[Cedarich]

PR description Implements global financing state and consistent server-error handling across the Project Portal.

• Adds a financing slice to the unified Zustand store managing credits, forward sales, payments, and payouts (with caching + backgrCound refresh).
• Adds optimistic update flows for key mutations (mint credits, create forward sale, initiate payment, distribute revenue) with rollback/failed-state handling.
• Refactors financing components to use the global slice instead of local useState .
• Implements a global 5xx error handler (Axios interceptor already existed; adds fetch-based handling and a global unhandled rejection guard) with branded toast feedback.
• Adds/updates tests for the financing slice and global 5xx handling.
• Fixes TypeScript diagnostics introduced during integration.
  Issues

Closes #329
Closes #334
closes #327

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[Cedarich]

@Oluwaseyi89