Enhance CSS animations and performance across seasonal styles; add will-change property for smoother transitions and optimize keyframes. [skip ci]

Jellyfin.Plugin.Seasonals/Web/filmnoir.css

@@ -22,8 +22,9 @@
 
 /* Film grain */
 .filmnoir-grain {
+    will-change: transform, opacity;
     position: absolute;
-    top: -50%;
+    top: 0;
     left: -50%;
     width: 200%;
     height: 200%;
@@ -32,6 +33,7 @@
     pointer-events: none;
     mix-blend-mode: overlay;
     opacity: 0.3;
+    translate: 0 -50vh;
 }
 
 /* Vignette */
@@ -48,6 +50,7 @@
 
 /* Occasional flicker and scratch */
 .filmnoir-scratches {
+    will-change: opacity;
     position: absolute;
     top: 0;
     left: 0;