- Introduce `BarrierManager` to handle neon cyberpunk-style barriers on screen edges and optional interior obstacles.
- Edge barriers blink in after a short delay, trap the player if they are inside when solidified (instant death + respawn), and explode when zone waves complete to allow exit.
- Interior barriers block enemies but not the player, adding tactical depth to arena layouts.
- Update `zones.json` with `interiorBarriers` config per zone.
- Adjust player/enemy sprite depths for correct rendering order relative to barriers.
- Integrate barrier collision into physics: player vs all barriers, enemies vs interior only; bullets destroyed on contact with any barrier.
- Refactor zone transitions and exit logic to coordinate barrier activation/destruction animations.
