feat: Smooth change in colour, no hard cut

Added option smoothing on colour change so there is no hard cut made when switching subjects

src/types/storage.ts

@@ -43,6 +43,7 @@ export interface SettingsState {
   iconOnlySidebar?: boolean;
   adaptiveThemeColour?: boolean;
   adaptiveThemeGradient?: boolean;
+  adaptiveThemeColourTransition?: boolean;
 
   // depreciated keys
   animatedbk: boolean;