Enable infinite signature navigation and improve button logic

Updated the `disabled` attribute logic in `EnvelopeViewer.razor`
to ensure navigation buttons are always active when signatures
exist. Modified `pdf-viewer.js` to enable infinite looping for
signature navigation, allowing users to cycle between the first
and last signatures seamlessly. Adjusted `canGoPrev` and
`canGoNext` properties to depend on the total number of
signatures, ensuring navigation is always enabled when
signatures are present.

EnvelopeGenerator.ReceiverUI/wwwroot/js/pdf-viewer.js

@@ -509,9 +509,9 @@ window.pdfViewer = {
             total: total,
             signed: signed,
             unsigned: unsigned,
-            currentIndex: signed,           // Sonraki imzan?n index'i
-            canGoPrev: signed > 0,          // En az 1 imza uygulanm?? m??
-            canGoNext: unsigned > 0         // Hala imzalanmam?? var m??
+            currentIndex: signed,
+            canGoPrev: total > 0,           // Her zaman aktif (e?er imza varsa)
+            canGoNext: total > 0            // Her zaman aktif (e?er imza varsa)
         };
     },
 
@@ -533,9 +533,11 @@ window.pdfViewer = {
         }
         
         // Bir sonraki imzay? al (imzalanm?? olup olmad???na bakmadan)
-        const nextIndex = currentIndex + 1;
+        let nextIndex = currentIndex + 1;
+        
+        // Sonsuz döngü: Son imzadaysa ilk imzaya dön
         if (nextIndex >= this._allSignatures.length) {
-            return false; // Son imzaday?z
+            nextIndex = 0;  // ?lk imzaya dön
         }
         
         const nextSignature = this._allSignatures[nextIndex];
@@ -608,9 +610,11 @@ window.pdfViewer = {
         }
         
         // Bir önceki imzay? al
-        const prevIndex = currentIndex - 1;
+        let prevIndex = currentIndex - 1;
+        
+        // Sonsuz döngü: ?lk imzadaysa son imzaya git
         if (prevIndex < 0) {
-            return false; // ?lk imzaday?z
+            prevIndex = this._allSignatures.length - 1;  // Son imzaya git
         }
         
         const prevSignature = this._allSignatures[prevIndex];