feat: Implement Local Storage for Notes

[evildead23151]

Description

Currently, transcribed notes are only held in the app's state and are lost when the app closes. This issue is about implementing a persistent storage solution to save journal entries on the user's device.

We will use @react-native-async-storage/async-storage, which is the community-standard key-value storage system for React Native.

Task

1. Create a set of utility functions in a new file, lib/storage.ts, for saving and retrieving notes. These functions will interact with AsyncStorage.
2. Modify the handleSave function in the NewEntryScreen (app/(tabs)/add.tsx) to call the new save function.
3. When saving, each note should be an object with at least these properties: id, date, transcript.

Acceptance Criteria

• A new note is successfully saved to AsyncStorage when the "Save" button is pressed.
• The note object must include a unique ID (e.g., using Date.now()) and a timestamp.
• The app must ask for no new permissions.
• The functions in lib/storage.ts should be well-documented.