[Workers] Fix callout and code langs (#17158)

current: https://developers.cloudflare.com/workers/frameworks/framework-guides/nextjs/#existing-nextjs-apps

Author: o-az

src/content/docs/workers/frameworks/framework-guides/nextjs.mdx

@@ -17,13 +17,13 @@ import {
 
 To create a new Next.js app, pre-configured to run on Cloudflare using [`@opennextjs/cloudflare`](https://opennext.js.org/cloudflare), run:
 
-```
+```sh
 npm create cloudflare@latest --no-auto-update --experimental --framework next
 ```
 
 #### Existing Next.js apps
 
-::: note
+:::note
 Minimum required Wrangler version: 3.78.10. Check your version by running `wrangler version`. To update Wrangler, refer to [Install/Update Wrangler](/workers/wrangler/install-and-update/).
 :::
 
@@ -77,13 +77,13 @@ To enable caching, you must:
 
 ##### Create a KV namespace
 
-```
+```sh
 npx wrangler@latest kv namespace create NEXT_CACHE_WORKERS_KV
 ```
 
 ##### Add the KV namespace to your Worker
 
-```
+```toml
 [[kv_namespaces]]
 binding = "NEXT_CACHE_WORKERS_KV"
 id = "<YOUR_NAMESPACE_ID>"