Add Animated Snake Death Effect

Instead of instantly stopping the game, animate the snake when it dies (e.g., fade out, flash red, break up into segments).

**Tasks:**
- Brainstorm and design a simple animation (CSS or Canvas).
- Trigger effect upon wall or self collision.
- Ensure the effect doesn't interfere with game logic.

**Why:**
Fun way for beginners to learn about canvas animations or CSS transitions!