Design and implement scene loading cancellation/escape mechanism

## Task

Research and implement the best approach for allowing users to cancel or escape from scene loading.

## Context

Currently, users are blocked by the loading screen when downloading large scenes (like Genesis Plaza). We need to determine the best UX pattern and implement it.

## Options to Evaluate

1. **Jump to another scene** - Allow map navigation to a different location while current scene is loading
2. **Keep main UI accessible** - Never fully hide UI elements (chat, map, settings, menu) during loading
3. **Explicit cancel button** - Add a "Cancel" or "Stop Loading" action
4. **Combination approach** - Mix of the above

## Scope

- [ ] Research and decide on best approach
- [ ] Design the UX flow
- [ ] Implement the chosen solution
- [ ] Test with large scenes (Genesis Plaza)
- [ ] Ensure no edge cases with scene state management

## Related

- #830 (proposal to enable UI interactions during loading)

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Requested by Pablo.​dcl.​eth via Slack