refactor: handle callingUserId consistently in GetSimilarUrlsForUrlUseCase

Co-authored-by: aider (anthropic/claude-sonnet-4-20250514) <[e-mail]>

src/modules/search/application/useCases/queries/GetSimilarUrlsForUrlUseCase.ts

···
     thumbnailUrl?: string;
   };
   urlLibraryCount: number;
-  urlInLibrary?: boolean;
+  urlInLibrary: boolean;
 }
 
 export interface GetSimilarUrlsForUrlResult {

src/modules/search/domain/services/SearchService.ts

···
         const urlLibraryCount = librariesResult.totalCount;
         
         // Check if calling user has this URL in their library
-        let urlInLibrary = false;
-        if (callingUserId) {
-          urlInLibrary = librariesResult.items.some(
-            (library) => library.userId === callingUserId,
-          );
-        }
+        // Default to false if no calling user (unauthenticated request)
+        const urlInLibrary = callingUserId
+          ? librariesResult.items.some(
+              (library) => library.userId === callingUserId,
+            )
+          : false;
 
         return {
           url: result.url,