Pre-Fetch: Scene Not Found Modal

## **⚠️ Problem:**
Player enters an invalid destination and we drop the loading screen + offload the current scene before knowing there is nothing to load — they land in a black screen or a hang instead of getting told. Costs Playtime; drop-off number unknown.

## **🏁 Scope:**
Define the modal shown at the pre-fetch step, before loading screen triggers and before current scene offloads. Copy, states, actions, per case. Visual design + implementation split into follow-up issues.

## **📝 Deliverables:**
- [ ] Define modal messages: out-of-bounds coords, empty parcel, world not found, fetch failed/offline
- [ ] Copy per state — title, body, error code visibility
- [ ] Actions per state
- [ ] Define cancel path: current scene stays loaded, no loading screen, no offload
- [ ] Define pre-fetch resolve timeout before modal shows
- [ ] Name `SCREEN_VIEW` event `INVALID_DESTINATION_MODAL_SHOW` + failure-reason property
- [ ] File implementation issue linking these specs

## **🔗 References:**
- [decentraland/godot-explorer#2698](https://github.com/decentraland/godot-explorer/issues/2698) — pre-fetch step this modal hooks into; metadata resolved before loading screen shows
- [decentraland/godot-explorer#2473](https://github.com/decentraland/godot-explorer/issues/2473) — cached empty parcel never resolves the loading screen; this modal is the pre-emptive fix
- [decentraland/godot-explorer#1156](https://github.com/decentraland/godot-explorer/issues/1156) — Teleport to Scene & World modal, Figma Modals file to extend
- No prior art in unity-explorer or docs (searched invalid destination, world not found, empty parcel teleport, 2026-08-21)