Apply optimistic learning-progress updates with reconciliation

[RUKAYAT-CODER]

Background

Progress updates block on the network before reflecting in the UI. Apply optimistically and reconcile on response.

Files to modify (2-3)

src/hooks/useLearningProgress.ts
src/services/offlineApi.ts

Acceptance Criteria

Implemented across the listed files

Unit/integration tests added or updated and passing

No regression; follows project coding standards