- Replace fragmented storage backends with single IndexedDBStorageBackend
- Create multi-store StorageBackend interface (storeName parameter)
- Remove old backends: IndexedDBBackend, LocalStorageBackend, SessionIndexedDBBackend, WebExtensionStorageBackend
- Remove old repositories: ProviderKeysRepository, SessionRepository, SettingsRepository
- Simplify AppStorage to directly expose storage methods (getSetting/setSetting, getProviderKey/setProviderKey)
- Create SessionsRepository for session-specific operations
- Update all consumers to use new simplified API
- Update example app to use new storage architecture
- Benefits: 10GB+ quota (vs 10MB chrome.storage), single database, consistent API
