Neon Sky Platformer

Create a polished single-file HTML5 platformer called Neon Sky Platformer.

Hard constraints:
- Embedded HTML/CSS/JS only; no external assets, analytics, APIs, or network calls.
- Playable on desktop and mobile.
- Load quickly and show a meaningful first screen within a few seconds.

Creative direction:
- Neon skyline, soft sunset gradients, glowing coins, readable platforms, and a compact arcade HUD.
- You may choose the exact level layout and camera behavior if it improves playability.

Core gameplay:
- Run, jump, double-jump, collect combo coins, avoid hazards, and reach a clear finish goal.
- Include moving platforms, fair enemy or spike patterns, checkpoints, score, lives, combo meter, start screen, win/game-over states, and restart.
- Controls: Arrow keys or A/D to move, Space to jump, R to restart, plus touch buttons for mobile.

Quality gates:
- The game must be playable, not a static scene.
- Collision should feel fair.
- The first 20 seconds should clearly teach the loop without a long tutorial.