Tail now uses the same approach as head: interpolated in the body path
from its previous position, with ease-in (mirror of head's ease-out).
Ghost circle removed — no longer needed since tail is naturally smooth.
Added EaseInCubic to AnimationHelper. InterpolatePosition now uses
string easing mode instead of bool.
When snake doesn't grow, the last segment (new tail) should interpolate
from the old tail's position (previous[segmentIndex]), not from the
second-to-last segment (previous[segmentIndex-1]) which didn't move.
- Two-timer architecture: game timer + 60fps render timer for smooth interpolation
- Snake body: StreamGeometry path with teal gradient, rounded joins
- Directional head with white eyes and dark pupils
- Food: pulsating glow, highlight, green leaf animation
- Modern dark theme (#0D1117), glassmorphism HUD
- Speed indicator bar, score +N popup
- High score persistence to JSON
- All keyboard shortcuts: Arrows, WASD, Space/P pause, Enter start, R restart, Esc quit
- Window resizable, 640x540 default
New files: AnimationHelper.cs, HighScoreManager.cs, SnakeRenderer.cs
