Clean up debugging code and refine error handling

Removed unnecessary `console.log` statements from `pdf-viewer.js`
and `receiver-signature.js` to reduce console output in production.
Simplified error handling in `pdf-viewer.js` for better clarity,
including consolidating error logging and removing redundant
handling for `RenderingCancelledException`.

Deleted the `debugDumpViewerDom` function and its public API
reference from `receiver-signature.js` as part of a cleanup
effort to eliminate unused debugging utilities. Streamlined
code related to event listener management in `pdf-viewer.js`
while retaining core functionality.

EnvelopeGenerator.ReceiverUI/wwwroot/js/receiver-signature.js

@@ -216,18 +216,6 @@ window.receiverSignature = (() => {
         overlayButtons.set(annotationId, { btn: wrapper, signed: isChecked });
     }
 
-    function debugDumpViewerDom() {
-        const wrapper = document.querySelector(VIEWER_WRAPPER_SEL);
-        if (!wrapper) { console.warn('[annot] .receiver-viewer-wrapper not found'); return; }
-        console.group('[annot] viewer DOM snapshot');
-        const cs = new Set();
-        wrapper.querySelectorAll('*').forEach(el => el.classList.forEach(c => cs.add(c)));
-        console.log('classes:', [...cs].sort().join(', '));
-        console.log('scroll container:', document.querySelector(SCROLL_CONTAINER_SEL));
-        console.log('page images:', document.querySelectorAll(PAGE_IMG_SEL));
-        console.groupEnd();
-    }
-
     // ?? Signature Pad ???????????????????????????????????????????????????????
 
     function _pos(canvas, event) {
@@ -332,7 +320,6 @@ window.receiverSignature = (() => {
     return {
         startTyped:                  startTyped,
         installAnnotationCheckboxes: installAnnotationCheckboxes,
-        debugDumpViewerDom:          debugDumpViewerDom,
         initialize:                  initialize,
         initializeTyped:             initializeTyped,
         initializeImage:             initializeImage,