[squad:plan] Echo Bloom — Playable Demo

**Owner:** McManus (Build & Release), with Verbal (Docs/Narrative) support

Milestone deliverables:
- Ship 8–10 chambers with onboarding
- Add save/load, settings, and a performance pass
- Prepare store page trailer copy, screenshots, and a feedback capture flow

Part of the Echo Bloom game plan (#54786).

The issue provides milestone deliverables but names no files, tests, or entry points. Start with the broader Echo Bloom game plan in #54786; completion requires the listed chambers, onboarding, save/load, settings, performance work, and store-feedback materials.

Written by the indexing model from the issue text.