Refactor PDF editor styles and add throttling logic

Refactored `SenderPdfImageEditor.razor` to use culture-invariant formatting for dynamic styles and introduced the `GetPageCanvasStyle` method for calculating `aspect-ratio` and `cursor` styles. Enhanced layout control with additional CSS properties.

Updated `envelope-editor.js` to include a throttling mechanism for mouse movement events using `_moveThrottle` and `requestAnimationFrame`. Added `getClickCoordsOnPdfPageThrottled` with a promise-based approach to improve performance during rapid interactions.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/js/envelope-editor.js

@@ -1,5 +1,11 @@
 window.envelopeEditor = {
 
+    _moveThrottle: {
+        rafId: 0,
+        latest: null,
+        waiters: []
+    },
+
     /**
      * Returns the click position normalised to [0,1] relative to the rendered PDF page
      * element inside DxPdfViewer (or DxReportViewer as fallback).
@@ -93,5 +99,33 @@ window.envelopeEditor = {
             pageIndex: targetIndex,
             pageNumber: parseInt(targetPage.getAttribute('data-editor-page') || String(targetIndex + 1), 10)
         };
+    },
+
+    getClickCoordsOnPdfPageThrottled: function (viewerCssClass, clientX, clientY) {
+        return new Promise((resolve) => {
+            const state = window.envelopeEditor._moveThrottle;
+            state.latest = { viewerCssClass, clientX, clientY };
+            state.waiters.push(resolve);
+
+            if (state.rafId !== 0) {
+                return;
+            }
+
+            state.rafId = window.requestAnimationFrame(() => {
+                state.rafId = 0;
+
+                const args = state.latest;
+                state.latest = null;
+
+                const result = args
+                    ? window.envelopeEditor.getClickCoordsOnPdfPage(args.viewerCssClass, args.clientX, args.clientY)
+                    : null;
+
+                const waiters = state.waiters.splice(0, state.waiters.length);
+                for (const waiter of waiters) {
+                    waiter(result);
+                }
+            });
+        });
     }
 };