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.

lib/auth.ts

@@ -55,6 +55,7 @@ export const { handlers, signIn, signOut, auth } = NextAuth({
   },
   pages: {
     signIn: '/login',
+    signOut: '/signout',
   },
   callbacks: {
     async session({ session, token }) {