feat(sender-editor): use rendered page metadata for field placement

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Pages/SenderEditorPage.razor

@@ -14,6 +14,7 @@
 @inject AppVersionService AppVersion
 @inject ILogger<SenderEditorPage> Logger
 @inject DocumentService DocumentService
+@inject PdfRenderService PdfRenderService
 @inject ReceiverService ReceiverService
 @inject EnvelopeService EnvelopeService
 @inject IStringLocalizer<Resource> UiLocalizer
@@ -278,7 +279,7 @@
         {
             <SenderPdfImageEditor IsPlacementMode="@(_pendingReceiverForPlacement is not null)"
                                   PageCount="@_pageCount"
-                                  PageImageDataUrls="@_pageImageDataUrls"
+                                  Pages="@_pagePreviews"
                                   PdfDataUrl="@PdfDataUrl"
                                   Fields="@FieldOverlays"
                                   EditorClick="OnPdfAreaClickAsync"
@@ -471,7 +472,7 @@
     string? _errorMessage;
     byte[]? _originalPdfBytes;  // Pristine upload — never modified, used as base for redraw
     int _pageCount;
-    Dictionary<int, string> _pageImageDataUrls = [];
+    List<PdfPageImageDto> _pagePreviews = [];
     int? _loadedEnvelopeId;
     int? _editingEnvelopeId;
     bool _isLoadingEnvelopeForEdit;
@@ -594,9 +595,11 @@
 
             _originalPdfBytes = document?.ByteData;
             _pdfLoaded = _originalPdfBytes is { Length: > 0 };
-            _pageCount = EstimatePdfPageCount(_originalPdfBytes) ??
-                Math.Max(1, _signatureFields.Select(f => f.Page).DefaultIfEmpty(1).Max());
-            _pageImageDataUrls.Clear();
+            _pagePreviews = [];
+            _pageCount = _pagePreviews.Count > 0
+                ? _pagePreviews.Count
+                : EstimatePdfPageCount(_originalPdfBytes)
+                    ?? Math.Max(1, _signatureFields.Select(f => f.Page).DefaultIfEmpty(1).Max());
             _fileName = $"Envelope-{envelopeId}.pdf";
             _pendingReceiverForPlacement = null;
             _loadedEnvelopeId = envelopeId;
@@ -638,8 +641,12 @@
             _originalPdfBytes = ms.ToArray();
             _fileName = file.Name;
             _pdfLoaded = true;
-            _pageCount = EstimatePdfPageCount(_originalPdfBytes) ?? 1;
-            _pageImageDataUrls.Clear();
+            _pagePreviews = (await PdfRenderService.RenderPagesAsync(_originalPdfBytes))
+                .OrderBy(p => p.PageNumber)
+                .ToList();
+            _pageCount = _pagePreviews.Count > 0
+                ? _pagePreviews.Count
+                : EstimatePdfPageCount(_originalPdfBytes) ?? 1;
             _signatureFields.Clear();
             _pendingReceiverForPlacement = null;
 
@@ -682,10 +689,10 @@
             return;
         }
 
-        // Approximate points based on A4. This is temporary until the image-based viewer
-        // pipeline provides precise per-page dimensions.
-        const double pageWidthPt = 595.0;
-        const double pageHeightPt = 842.0;
+        int page1Based = coords.PageIndex + 1;
+        var pagePreview = _pagePreviews.FirstOrDefault(p => p.PageNumber == page1Based);
+        var pageWidthPt = pagePreview?.WidthPt ?? 595.0;
+        var pageHeightPt = pagePreview?.HeightPt ?? 842.0;
 
         // Convert normalised [0,1] → PDF points; clamp so box stays inside page
         double xPt = coords.NormX * pageWidthPt;
@@ -694,8 +701,6 @@
         xPt = Math.Max(0, Math.Min(xPt, pageWidthPt - SigWidthPt));
         yPt = Math.Max(0, Math.Min(yPt, pageHeightPt - SigHeightPt));
 
-        int page1Based = coords.PageIndex + 1;
-
         var field = new SignatureFieldDraft(
             XPt: xPt,
             YPt: yPt,