Build "Echo Runner" Game

### Project slug (e.g., snake, todo)

_No response_

### Summary

Create a side-scrolling runner game where each attempt records your movement (jump timing). The next run replays your previous “echoes” as obstacles. Survive as long as possible!

**Acceptance Criteria:**

- Auto-scroll background.

- Space key or click makes the player jump.

- Ghost echoes appear from past runs.

- Collision with ghosts ends the game.

**Optional Enhancements:**

- Add speed increase over time.

- Display ghost trails fading in/out.

### Details / Acceptance criteria

_No response_

### Scope

- [ ] UI changes
- [ ] Logic changes
- [ ] Accessibility
- [ ] Tests (manual)