fix: add null coalescing check for context param in Gutenberg.php

Add null coalescing operator to check for context parameter existence
before accessing it in extend_post_content method. This prevents PHP 8+
"Undefined array key" warnings that corrupt JSON responses when the
context query parameter is not explicitly provided in REST API requests.

Fixes #940

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: devinle

.changeset/fix-undefined-context-key.md

@@ -0,0 +1,5 @@
+---
+"@headstartwp/headstartwp": patch
+---
+
+Fix: Add null coalescing check for context parameter in extend_post_content to prevent PHP 8+ "Undefined array key" warning. Fixes #940

wp/headless-wp/includes/classes/Integrations/Gutenberg.php

@@ -87,7 +87,7 @@ public function extend_post_content( \WP_REST_Response $data, \WP_Post $post, \W
 
 		$params = $request->get_params();
 
-		if ( 'view' !== $params['context'] ) {
+		if ( 'view' !== ( $params['context'] ?? '' ) ) {
 			return $data;
 		}