fix: split mixed shell/js code blocks in Next.js push guide

Separating shell and javascript into distinct Code blocks prevents
selecting the shell tab from breaking js-only code blocks on the page.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: maratal

src/pages/docs/push/getting-started/nextjs.mdx

@@ -342,7 +342,7 @@ Navigate to `http://localhost:3000/push` in your browser. Click **Activate Push*
 
 ### Test push notifications <a id="step-3-test"/>
 
-Once the device is activated, send a test push notification directly to your client ID using the Ably CLI or from code:
+Once the device is activated, send a test push notification directly to your client ID using the Ably CLI:
 
 <Code>
 ```shell
@@ -351,7 +351,11 @@ ably push publish --client-id push-tutorial-client \
   --body "Hello from CLI!" \
   --data '{"foo":"bar"}'
 ```
+</Code>
+
+Or from code:
 
+<Code>
 ```javascript
 await client.push.admin.publish(
   { clientId: 'push-tutorial-client' },
@@ -371,7 +375,9 @@ ably push publish --device-id <your-device-id> \
   --title "Test push" \
   --body "Hello from CLI!"
 ```
+</Code>
 
+<Code>
 ```javascript
 await client.push.admin.publish(
   { deviceId: client.device().id },
@@ -458,7 +464,7 @@ export function ChannelSubscription({ onLog }: { onLog: (msg: string) => void })
 
 `usePush` returns `isActivated` — a reactive boolean shared with `usePushActivation` via a module-level store. When `PushActivationBanner` calls `activate()`, all `usePush` instances update automatically, so the subscribe buttons enable without any extra wiring.
 
-To test channel push, subscribe to the channel in the UI then send a push notification to the channel using the Ably CLI or from code:
+To test channel push, subscribe to the channel in the UI then send a push notification to the channel using the Ably CLI:
 
 <Code>
 ```shell
@@ -467,7 +473,11 @@ ably push publish --channel exampleChannel1 \
   --body "Hello from CLI!" \
   --data '{"foo":"bar"}'
 ```
+</Code>
 
+Or from code:
+
+<Code>
 ```javascript
 await channel.publish({
   name: 'example',