docs(js): Add Next.js build option disableManifestInjection (#14362)

Author: chargome

docs/platforms/javascript/guides/nextjs/configuration/build/index.mdx

@@ -254,6 +254,20 @@ Automatically create cron monitors in Sentry for your Vercel Cron Jobs if config
 
 </SdkOption>
 
+<SdkOption name="disableManifestInjection" type="boolean|undefined" defaultValue="false">
+
+Disables automatic injection of the route manifest into the client bundle.
+
+The route manifest is a build-time generated mapping of your Next.js App Router routes that enables Sentry to group transactions by parameterized route names (e.g., `/users/:id` instead of `/users/123`, `/users/456`, etc.).
+
+**Disable this option if:**
+- You want to minimize client bundle size
+- You're experiencing build issues related to route scanning
+- You prefer raw URLs in transaction names
+- You're only using the Pages Router (this feature is only supported in the App Router)
+
+</SdkOption>
+
 <SdkOption
   name="unstable_sentryWebpackPluginOptions"
   type="SentryWebpackPluginOptions"