UX: Improve appearance and handling of accepted answers without excerpts

- Hide blockquote for accepted answers without excerpts to avoid unnecessary visual elements.
- Adjust title padding for better alignment when excerpts are absent.
- Ensure no content fallback (`""`) when excerpts are not provided.
- Add `accepted-answer--has-excerpt` class for proper styling differentiation.

assets/javascripts/discourse/components/solved-accepted-answer.gjs

@@ -29,7 +29,7 @@ export default class SolvedAcceptedAnswer extends Component {
 
   get collapsedContent() {
     if (!this.hasExcerpt) {
-      return null;
+      return "";
     }
 
     return htmlSafe(this.acceptedAnswer.excerpt);
@@ -89,6 +89,7 @@ export default class SolvedAcceptedAnswer extends Component {
       <PostQuotedContent
         class={{concatClass
           "accepted-answer"
+          (if this.hasExcerpt "accepted-answer--has-excerpt")
           (unless this.collapsedContent "title-only")
         }}
         @collapsedContent={{this.collapsedContent}}