[Feature]: Offline Functionality

### Problem to solve

As an astronomy enthusiast, I want to be able to access a lot of the features of the application while not connected to the internet, as I may be in locations where I don't have service.

### Desired outcome

Users would be able to see at least the main features of the application while out of service.

### Proposed solution

_No response_

### Alternatives considered

_No response_

### Additional context

_No response_

### Before submitting

- [x] I searched existing issues and did not find an equivalent request.

The issue names no files, tests, or entry points, so first map the application's main features and how they depend on network access. Clarify which features must work offline and how offline behavior will be tested; done means the agreed core features remain usable without service.

Written by the indexing model from the issue text.