fix(hooks): add robust MIME type handling and Wikipedia download checks

backend/pb_hooks/fetch_covers.pb.js

@@ -83,9 +83,16 @@ onRecordAfterCreateRequest((e) => {
             console.log("Ostatecznie pobieram wybraną okladke z sieci...");
             const imgRes = $http.send({
                 url: thumbUrl,
-                method: "GET"
+                method: "GET",
+                headers: { 
+                    "Accept": "image/jpeg, image/png, image/webp, image/gif, image/*;q=0.8"
+                }
             });
 
+            if (imgRes.statusCode !== 200) {
+                throw new Error(`Pobieranie obrazka nie powiodło się, kod statusu: ${imgRes.statusCode}`);
+            }
+
             const safeTitle = title.replace(/[^a-z0-9]/gi, '_').toLowerCase();
             let ext = ".jpg";
             const lowerThumbUrl = thumbUrl.toLowerCase();