Refactor Async Workflow UI States

[Siddharthakhandelwal]

Users require clear progress metrics and actionable errors across multiple steps of the sequence-to-insight journey.
Tasks/Acceptance Criteria:

• Create a single source of truth in App.jsx (maybe via useReducer or a custom hook usePredictionWorkflow) indicating the active sub-state.
• Supported Workflow States: idle, loading, predicting, parsing, rendering, succeeded, failed.
• Map these stages clearly on the UI using current skeleton loaders and statuses.
• Wire any failed stage mapping to display a toast message exposing a user retry option.