templates: fix experimental-build-mode compile generating invalid code (#13828)

When using `pnpm next build --experimental-build-mode compile` in our
website template, Next.js outputs the following code:

<img width="2322" height="1262" alt="Screenshot 2025-09-16 at 14 39
31@2x"
src="https://github.com/user-attachments/assets/bb7dc5c1-ffe7-4ee7-8864-19cb2147c07d"
/>

If you then run `pnpm next build --experimental-build-mode generate` or
`pnpm next build --experimental-build-mode generate-env` which inlines
the env variable, it becomes the following code:

<img width="2276" height="1340" alt="Screenshot 2025-09-16 at 14 40
14@2x"
src="https://github.com/user-attachments/assets/6fc8cbd4-4df8-4d9b-a3e5-fc299e147537"
/>

Suddenly, it no longer assigns to a variable but to a string, which is
invalid JavaScript syntax, throwing the following error:

<img width="2314" height="320" alt="Screenshot 2025-09-16 at 14 40
53@2x"
src="https://github.com/user-attachments/assets/2c3487be-82e3-4043-aa04-0d98f0a05b4b"
/>

This PR works around this issue changing up the source code in
`getServerSideURL`.

I have reported this issue to Next.js:
vercel/next.js#83863


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Author: AlessioGr

templates/website/src/utilities/getURL.ts

@@ -1,17 +1,12 @@
 import canUseDOM from './canUseDOM'
 
 export const getServerSideURL = () => {
-  let url = process.env.NEXT_PUBLIC_SERVER_URL
-
-  if (!url && process.env.VERCEL_PROJECT_PRODUCTION_URL) {
-    return `https://${process.env.VERCEL_PROJECT_PRODUCTION_URL}`
-  }
-
-  if (!url) {
-    url = 'http://localhost:3000'
-  }
-
-  return url
+  return (
+    process.env.NEXT_PUBLIC_SERVER_URL ||
+    (process.env.VERCEL_PROJECT_PRODUCTION_URL
+      ? `https://${process.env.VERCEL_PROJECT_PRODUCTION_URL}`
+      : 'http://localhost:3000')
+  )
 }
 
 export const getClientSideURL = () => {

templates/with-vercel-website/src/utilities/getURL.ts

@@ -1,17 +1,12 @@
 import canUseDOM from './canUseDOM'
 
 export const getServerSideURL = () => {
-  let url = process.env.NEXT_PUBLIC_SERVER_URL
-
-  if (!url && process.env.VERCEL_PROJECT_PRODUCTION_URL) {
-    return `https://${process.env.VERCEL_PROJECT_PRODUCTION_URL}`
-  }
-
-  if (!url) {
-    url = 'http://localhost:3000'
-  }
-
-  return url
+  return (
+    process.env.NEXT_PUBLIC_SERVER_URL ||
+    (process.env.VERCEL_PROJECT_PRODUCTION_URL
+      ? `https://${process.env.VERCEL_PROJECT_PRODUCTION_URL}`
+      : 'http://localhost:3000')
+  )
 }
 
 export const getClientSideURL = () => {