Implement Offline Reading Capability

[RomanTsisyk]

As a user,
I want to save articles for offline reading,
So that I can access content without an internet connection.

Acceptance Criteria

1. Save for Offline: A 'Save for Offline' button should be visible and accessible on each article's detail screen.
2. Article Retrieval: When a user selects the 'Save for Offline' option, the article should be downloaded and stored locally on the device.
3. Offline Access: Users should be able to access their saved articles from a dedicated 'Offline Articles' section in the app, available from the main navigation.
4. Notification: After an article is saved for offline reading, the user should receive a confirmation notification in the app indicating successful saving.
5. Storage Management: Users should be able to view the amount of device storage used by the app and delete offline articles as needed.

Additional Notes

1. Ensure that the offline storage does not significantly impact the device’s overall performance and storage capacity.
2. The UI for offline articles should match the design and user experience of the rest of the app.
3. Consider implementing a background service for managing downloads to prevent any disruptions in user experience.

Tasks Breakdown

1. UI Implementation: Design and implement the 'Save for Offline' button and the 'Offline Articles' section.
2. Database Management: Set up the Room database for storing articles and managing space efficiently.
3. Testing: Ensure that all acceptance criteria are met through thorough testing, including unit tests and UI tests.