Add support for saving articles while offline

[RayBB]

Currently, it's not possible to save new articles to Frigoligo while offline. This limits the app's offline-first capabilities, especially when users want to save linked articles while reading offline.

Proposed solution:

• Add ability to queue article saves while offline
• Store article URLs and metadata (like date added) locally when saved offline
• Automatically sync queued articles when connection is restored

This enhancement aligns with Frigoligo's offline-first philosophy and would improve the reading experience by allowing users to:

• Save interesting links they find while reading offline or poor connection
• Continue their reading flow without interruption
• Have articles automatically download when connectivity returns