Refactor UI imports and update component paths

Replaces imports from 'components/ui' with 'components/common' across the app and dashboard pages, and updates model and API imports to use new paths under 'lib'. Removes redundant authentication checks from several dashboard pages. Adds new dashboard components and utility files, and reorganizes hooks and services into the 'lib' directory for improved structure.

components/layout/theme-switcher.tsx

@@ -0,0 +1,30 @@
+"use client";
+
+import { useTheme } from "next-themes";
+import { useEffect, useState } from "react";
+import { Button } from "@/components/common/button";
+
+export function ThemeSwitcher() {
+  const { theme, setTheme } = useTheme();
+  const [mounted, setMounted] = useState(false);
+
+  // Required for server-side rendering
+  useEffect(() => setMounted(true), []);
+
+  if (!mounted) return null;
+
+  return (
+    <Button
+      variant="ghost" 
+      size="icon"
+      onClick={() => setTheme(theme === "dark" ? "light" : "dark")}
+      className="ml-2"
+    >
+      {theme === "dark" ? (
+        <svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" className="lucide lucide-sun"><circle cx="12" cy="12" r="4"/><path d="M12 2v2"/><path d="M12 20v2"/><path d="m4.93 4.93 1.41 1.41"/><path d="m17.66 17.66 1.41 1.41"/><path d="M2 12h2"/><path d="M20 12h2"/><path d="m6.34 17.66-1.41 1.41"/><path d="m19.07 4.93-1.41 1.41"/></svg>
+      ) : (
+        <svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" className="lucide lucide-moon"><path d="M12 3a6 6 0 0 0 9 9 9 9 0 1 1-9-9Z"/></svg>
+      )}
+    </Button>
+  );
+}