Game Systems FTUE: Menu Tour + First-Session Reward

## **⚠️ Problem:**
New users that reach the world have with no introduction to Discover, Friends, Nearby, Profile, Backpack — nothing tells them what DCL is for hence drop early or game seems too shallow to come back for more, affecting Day 1 Retention.

## **🏁 Scope:**
A Systems FTUE that tours the 5 core menus on first session, then grants a reward on completion. Scene-agnostic — hookable from any scene, skippable, once per install.

## **📝 Deliverables:**
- [ ] A visible starting point in HUD that triggers players to interact
- [ ] Tour UI across Discover, Friends, Nearby, Profile, Backpack
- [ ] Trigger + completion state hookable from any scene, once per install
- [ ] Reward granted on tour completion, claim surfaced in-app
- [ ] Skip and resume behavior defined
- [ ] `SCREEN_VIEW` per step + completion/skip events implemented

## Metrics
- Retention (D1).
- Baseline: 12% (UTC Based)
- Measure: per-step `SCREEN_VIEW` drop-off, completion rate, D1/D7 completers vs skippers, menu open rate first session.

## **🔗 References:**
- [decentraland/unity-explorer#7671](https://github.com/decentraland/unity-explorer/pull/7671) — desktop removed the onboarding startup op, "not planning on re-introducing the onboarding world" → no parity target, mobile builds net-new.
- [decentraland/unity-explorer#5724](https://github.com/decentraland/unity-explorer/issues/5724) — [Epic] Onboarding, closed not-planned. Desktop's model was a tutorial world, not a menu tour.
- [decentraland/godot-explorer#2553](https://github.com/decentraland/godot-explorer/pull/2553) — `reward_modal` + `reward_campaigns.gd`, signed POST `/api/rewards`. Reuse for the reward; grants only when campaign has `requires_catalyst = false`.
- [decentraland/godot-explorer#1900](https://github.com/decentraland/godot-explorer/issues/1900) — Discover FTUE screen + device-storage first-run flag. Precedent for once-per-install gating and the 23% figure.

## Notes
- Reward asset: wearable or emote? Which campaign key?
- Claim-anywhere campaign required (`requires_catalyst = false`) — who creates it?
- Tour fires after `DISCOVER_FTUE` or on first world entry?
- 5 menus in one sitting, or split across first sessions?