Fix auth redirect to use session email instead of hardcoded workspace

New users were being sent to /marks-account/projects. Now derives
workspace from the signed-in user's email so everyone lands on
their own workspace after Google OAuth.

Made-with: Cursor

app/components/NextAuthComponent.tsx

@@ -13,7 +13,7 @@ export default function NextAuthComponent() {
     try {
       // Sign in with Google using NextAuth
       await signIn("google", {
-        callbackUrl: "/marks-account/projects",
+        callbackUrl: "/auth",
       });
     } catch (error) {
       console.error("Google sign-in error:", error);