Cleanup: split offline store responsibilities and shared types

[enaboapps]

Summary

Break the offline storage layer into smaller modules with shared types and remove duplicated responsibilities.

Scope

• split bootstrap persistence and talk status persistence into separate files
• add a shared offline types module
• remove duplicate audio-clear logic from the offline store layer
• keep lib/offlineStore.ts as a compatibility facade during migration

Target Files

• lib/offlineStore.ts
• new lib/offlineBootstrapStore.ts
• new lib/offlineTalkStatusStore.ts
• new lib/offlineTypes.ts
• lib/audioStore.ts
• hooks/useOfflineBoot.tsx
• hooks/useOfflineLibrarySync.ts

Acceptance Criteria

• offline storage responsibilities are clearly separated
• no duplicate audio-clear implementation remains
• existing imports continue to work through the compatibility facade
• npm run build passes
• npm run lint passes