feat: refactor sign-in prompts to use SignedOutPanel component

frontend/src/app/board-groups/new/page.tsx

@@ -6,7 +6,7 @@ import { useState } from "react";
 import Link from "next/link";
 import { useRouter } from "next/navigation";
 
-import { SignInButton, SignedIn, SignedOut, useAuth } from "@/auth/clerk";
+import { SignedIn, SignedOut, useAuth } from "@/auth/clerk";
 
 import { ApiError } from "@/api/mutator";
 import {
@@ -16,6 +16,7 @@ import {
 } from "@/api/generated/boards/boards";
 import { useCreateBoardGroupApiV1BoardGroupsPost } from "@/api/generated/board-groups/board-groups";
 import type { BoardRead } from "@/api/generated/model";
+import { SignedOutPanel } from "@/components/auth/SignedOutPanel";
 import { DashboardSidebar } from "@/components/organisms/DashboardSidebar";
 import { DashboardShell } from "@/components/templates/DashboardShell";
 import { Button } from "@/components/ui/button";
@@ -126,16 +127,10 @@ export default function NewBoardGroupPage() {
   return (
     <DashboardShell>
       <SignedOut>
-        <div className="col-span-2 flex min-h-[calc(100vh-64px)] items-center justify-center bg-slate-50 p-10 text-center">
-          <div className="rounded-xl border border-slate-200 bg-white px-8 py-6 shadow-sm">
-            <p className="text-sm text-slate-600">
-              Sign in to create a board group.
-            </p>
-            <SignInButton mode="modal" forceRedirectUrl="/board-groups/new">
-              <Button className="mt-4">Sign in</Button>
-            </SignInButton>
-          </div>
-        </div>
+        <SignedOutPanel
+          message="Sign in to create a board group."
+          forceRedirectUrl="/board-groups/new"
+        />
       </SignedOut>
       <SignedIn>
         <DashboardSidebar />