feat: remove ModeToggle from Header, set Toaster theme to dark, and update global styles for consistent dark mode

apps/web/src/components/ui/sonner.tsx

@@ -1,11 +1,8 @@
 "use client";
 
-import { useTheme } from "next-themes";
 import { Toaster as Sonner, type ToasterProps } from "sonner";
 
 const Toaster = ({ ...props }: ToasterProps) => {
-  const { theme = "system" } = useTheme();
-
   return (
     <Sonner
       className="toaster group"
@@ -16,7 +13,7 @@ const Toaster = ({ ...props }: ToasterProps) => {
           "--normal-border": "var(--border)",
         } as React.CSSProperties
       }
-      theme={theme as ToasterProps["theme"]}
+      theme={"dark"}
       {...props}
     />
   );