offline mode when can't connect to sdk / internet

Nobody has claimed this yet.

## The Issue
We should allow the app to startup without a SDK connection in "offline mode". With numerous planned upgrades to the SDK, there may be times when an upgrade affects a large set of app users where they can't startup. If we allowed offline mode, they could at least startup and grab an update we would have pushed, otherwise, they need to manually download/install. Offline mode would also allow users to watch their downloaded content (probably needs file_list caching first).

## System Configuration

- LBRY Daemon version:
- LBRY App version:
- LBRY Installation ID:
- Operating system:

## Anything Else

## Screenshots

## Internal Use

### Acceptance Criteria
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### Definition of Done
- [ ] Tested against acceptance criteria
- [ ] Tested against the assumptions of the user story
- [ ] The project builds without errors
- [ ] Unit tests are written and passing
- [ ] Tests on devices/browsers listed in the issue have passed
- [ ] QA performed & issues resolved
- [ ] Refactoring completed
- [ ] Any configuration or build changes documented
- [ ] Documentation updated
- [ ] Peer Code Review performed

No files or tests are named. Start by tracing the app startup path and SDK connection handling; define the offline behavior around starting without an SDK connection, updating the app, and watching downloaded content, including the proposed file_list caching. Done means the app can start offline and support the stated recovery and playback use cases, with tests covering the acceptance criteria.

Written by the indexing model from the issue text.