feat: add workspace management features including member invitations and role updates

- Implemented API endpoints for managing workspace members (GET, POST, PATCH, DELETE).
- Added workspace creation and retrieval functionalities.
- Enhanced project model to associate with workspaces.
- Updated project member roles and access control logic.
- Created sign-out page and updated authentication flow.
- Modified header to include navigation to workspaces.
- Updated Prisma schema to include workspace and member models.
- Seed script updated to create demo workspaces and associated members.

app/signout/page.tsx

@@ -0,0 +1,40 @@
+'use client';
+
+import { useState } from 'react';
+import { signOut } from 'next-auth/react';
+import { LogOut } from 'lucide-react';
+import { Button } from '@/components/ui/button';
+import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
+
+export default function SignOutPage() {
+  const [loading, setLoading] = useState(false);
+
+  const handleSignOut = async () => {
+    setLoading(true);
+    await signOut({ callbackUrl: '/login' });
+  };
+
+  return (
+    <div className="min-h-screen flex items-center justify-center bg-background px-4">
+      <Card className="w-full max-w-sm">
+        <CardHeader className="text-center">
+          <div className="mx-auto mb-4 flex h-12 w-12 items-center justify-center rounded-full bg-muted">
+            <LogOut className="h-6 w-6 text-muted-foreground" />
+          </div>
+          <CardTitle className="text-2xl">Sign out</CardTitle>
+          <CardDescription>
+            Are you sure you want to sign out?
+          </CardDescription>
+        </CardHeader>
+        <CardContent className="flex flex-col gap-3">
+          <Button onClick={handleSignOut} disabled={loading} className="w-full">
+            {loading ? 'Signing out...' : 'Sign out'}
+          </Button>
+          <Button variant="outline" asChild className="w-full">
+            <a href="/dashboard">Cancel</a>
+          </Button>
+        </CardContent>
+      </Card>
+    </div>
+  );
+}