fix: resolve remaining PHPCS errors (4 violations across 3 files)

- Downgrade Generic.Files.OneObjectStructurePerFile to warning
  (widget class shares file with public class — split in future cleanup)
- Add translators comment for __() with %s placeholder in REST API
- Remove blank line after control structure in REST API
- Fix return-newline in content filter (extract to $prompt variable)

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

.phpcs.xml.dist

@@ -49,6 +49,9 @@
     <rule ref="Universal.Files.SeparateFunctionsFromOO">
         <type>warning</type>
     </rule>
+    <rule ref="Generic.Files.OneObjectStructurePerFile">
+        <type>warning</type>
+    </rule>
 
     <rule ref="WordPress-Extra">
         <!-- Don't require Yoda conditions for readability -->

includes/class-peptide-news-content-filter.php

@@ -398,8 +398,7 @@ class Peptide_News_Content_Filter {
 
 		// Use XML-style delimiters to isolate untrusted article data from the prompt.
 		// This mitigates prompt injection by clearly separating instructions from data.
-		return
-			"You are a content classifier. Your ONLY task is to classify the article below.\n" .
+		$prompt = "You are a content classifier. Your ONLY task is to classify the article below.\n" .
 			"Respond with EXACTLY one word: EDITORIAL or PROMOTIONAL.\n" .
 			"EDITORIAL = genuine news, research, or journalism.\n" .
 			"PROMOTIONAL = press releases, ads, sponsored content, product launches, " .
@@ -412,6 +411,7 @@ class Peptide_News_Content_Filter {
 			sprintf( "<content>%s</content>\n", $content_trimmed ) .
 			"</article_to_classify>\n\n" .
 			"Classification (one word only):";
+		return $prompt;
 	}
 
 	/**

includes/class-peptide-news-rest-api.php

@@ -114,6 +114,7 @@ class Peptide_News_Rest_API {
 		if ( ! preg_match( '/^\\d{4}-\\d{2}-\\d{2}$/', $value ) ) {
 			return new WP_Error(
 				'rest_invalid_date',
+				/* translators: %s: parameter name */
 				sprintf( __( 'Invalid date format for %s. Expected Y-m-d.', 'peptide-news' ), $param ),
 				array( 'status' => 400 )
 			);
@@ -184,7 +185,6 @@ class Peptide_News_Rest_API {
 					}
 				}
 			}
-
 		}
 
 		$data = array(