Use siteConfig instead of NEXT_PUBLIC_APP_URL for root layout metadata

The metadata in the root layout referenced process.env.NEXT_PUBLIC_APP_URL
with non-null assertions, but this env var is not guaranteed to be set
(only .env.example exists). This caused `new URL(undefined)` to throw
during SSR, resulting in a blank page on /create (and all other routes).

Replace all NEXT_PUBLIC_APP_URL references in metadata with siteConfig.url
and siteConfig.ogImage, which are already defined and used elsewhere in
the same metadata block.

https://claude.ai/code/session_01Ez3f6QxR3MxNq6YfAeqrcH

apps/v4/app/layout.tsx

@@ -20,7 +20,7 @@ export const metadata: Metadata = {
     default: siteConfig.name,
     template: `%s - ${siteConfig.name}`,
   },
-  metadataBase: new URL(process.env.NEXT_PUBLIC_APP_URL!),
+  metadataBase: new URL(siteConfig.url),
   description: siteConfig.description,
   keywords: ["Next.js", "React", "Tailwind CSS", "Components", "shadcn"],
   authors: [
@@ -33,13 +33,13 @@ export const metadata: Metadata = {
   openGraph: {
     type: "website",
     locale: "en_US",
-    url: process.env.NEXT_PUBLIC_APP_URL!,
+    url: siteConfig.url,
     title: siteConfig.name,
     description: siteConfig.description,
     siteName: siteConfig.name,
     images: [
       {
-        url: `${process.env.NEXT_PUBLIC_APP_URL}/opengraph-image.png`,
+        url: siteConfig.ogImage,
         width: 1200,
         height: 630,
         alt: siteConfig.name,
@@ -50,7 +50,7 @@ export const metadata: Metadata = {
     card: "summary_large_image",
     title: siteConfig.name,
     description: siteConfig.description,
-    images: [`${process.env.NEXT_PUBLIC_APP_URL}/opengraph-image.png`],
+    images: [siteConfig.ogImage],
     creator: "@shadcn",
   },
   icons: {