feat: refactor theme management and remove next-themes dependency

- Replaced the next-themes package with a custom ThemeProvider component for enhanced theme management.
- Implemented local storage handling for theme persistence and system theme detection.
- Updated the Toaster component to utilize the new theme context.
- Removed unused next-themes references from package.json and package-lock.json.

components/ui/sonner.tsx

@@ -1,6 +1,6 @@
 "use client"
 
-import { useTheme } from "next-themes"
+import { useTheme } from "@/components/theme-provider"
 import { Toaster as Sonner, type ToasterProps } from "sonner"
 
 const Toaster = ({ ...props }: ToasterProps) => {