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.Client/Components/PdfEditor/SenderPdfImageEditor.razor

@@ -1,5 +1,6 @@
 @using EnvelopeGenerator.Application.Resources
 @using EnvelopeGenerator.Application.Common.Dto
+@using System.Globalization
 @using Microsoft.Extensions.Localization
 @inject IStringLocalizer<Resource> UiLocalizer
 @inject IJSRuntime JSRuntime
@@ -39,7 +40,7 @@
                      data-page-height-pt="@heightPt">
                     <div class="sender-image-editor__page-canvas"
                          data-editor-page-canvas="@pageNumber"
-                         style="@( _isDragging ? "cursor:grabbing;" : string.Empty)">
+                         style="@GetPageCanvasStyle(widthPt, heightPt)">
                         @if (!string.IsNullOrWhiteSpace(pagePreview?.ImageDataUrl))
                         {
                             <img class="sender-image-editor__page-image"
@@ -117,15 +118,40 @@
         var widthPercent = (127.44 / pageWidthPt) * 100.0;
         var heightPercent = (141.12 / pageHeightPt) * 100.0;
 
+        var left = leftPercent.ToString("F4", CultureInfo.InvariantCulture);
+        var top = topPercent.ToString("F4", CultureInfo.InvariantCulture);
+        var width = widthPercent.ToString("F4", CultureInfo.InvariantCulture);
+        var height = heightPercent.ToString("F4", CultureInfo.InvariantCulture);
+
         return string.Join(' ',
-            $"left:{leftPercent:F4}%;",
-            $"top:{topPercent:F4}%;",
-            $"width:{widthPercent:F4}%;",
-            $"height:{heightPercent:F4}%;",
+            "position:absolute;",
+            $"left:{left}%;",
+            $"top:{top}%;",
+            $"width:{width}%;",
+            $"height:{height}%;",
+            "border:2px solid;",
+            "border-radius:8px;",
+            "display:flex;",
+            "align-items:flex-start;",
+            "justify-content:space-between;",
+            "gap:0.35rem;",
+            "padding:0.2rem 0.3rem;",
+            "overflow:hidden;",
+            "z-index:30;",
             $"border-color:{field.Color};",
             $"background-color:{field.Color}22;");
     }
 
+    private string GetPageCanvasStyle(double pageWidthPt, double pageHeightPt)
+    {
+        var ratio = pageHeightPt <= 0 ? 595.0 / 842.0 : pageWidthPt / pageHeightPt;
+        var ratioText = ratio.ToString("F6", CultureInfo.InvariantCulture);
+        var cursor = _isDragging
+            ? "grabbing"
+            : (IsPlacementMode ? "crosshair" : "default");
+        return $"aspect-ratio:{ratioText};cursor:{cursor};";
+    }
+
     private async Task HandleClickAsync(MouseEventArgs args)
     {
         if (EditorClick.HasDelegate)
@@ -182,7 +208,7 @@
         await MoveField.InvokeAsync(new SenderPdfFieldMoveRequest(_draggedFieldIndex.Value, pageNumber, xPt, yPt));
     }
 
-    private void OnEditorMouseUp(MouseEventArgs _)
+    private void OnEditorMouseUp(MouseEventArgs args)
     {
         _draggedFieldIndex = null;
         _isDragging = false;