Add Loading States

## Description\nImprove UX by adding loading states to async operations.\n\n**Acceptance Criteria:**\n- Loading spinners\n- Skeleton loaders\n- Disabled buttons during submission\n- Error states

Start by locating the frontend's asynchronous operations and their submission controls; the issue does not name specific files, components, or tests. Review the existing UX patterns before implementing the requested loading spinners, skeleton loaders, disabled submission buttons, and error states, then verify each affected operation visibly handles loading, submission, and failure.

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