Add dynamic color support for receivers

Introduced a `Color` property to `ReceiverDraft` and `SignatureFieldDraft` models, enabling dynamic color assignment from a predefined palette (`ReceiverPalette`). Updated the UI to reflect receiver-specific colors in the sender-receiver chips, placement mode hint bar, and signature placement button.

Refactored PDF rendering logic to dynamically derive visual styles (fill, border, and text colors) from receiver colors. Added a `HexToXColor` utility for converting hex color strings to `PdfSharp.Drawing.XColor`.

Removed hardcoded visual styles and replaced them with dynamic, receiver-specific styling. Simplified receiver addition logic to automatically assign colors from the palette. These changes improve clarity and maintainability while enhancing the user experience.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Components/Pages/EnvelopeSenderEditorPage.razor

@@ -74,7 +74,8 @@
                         <div class="sender-receivers-list">
                             @foreach (var receiver in _receivers)
                             {
-                                <div class="sender-receiver-chip">
+                        <div class="sender-receiver-chip"
+                             style="border-left: 3px solid @receiver.Color;">
                                     <div class="sender-receiver-chip__body">
                                         <div class="sender-receiver-chip__name">@receiver.FullName</div>
                                         <div class="sender-receiver-chip__email">@receiver.Email</div>
@@ -87,6 +88,7 @@
                                     <button class="pdf-toolbar__btn pdf-toolbar__btn--signature-change sender-toolbar-action-btn sender-toolbar-action-btn--compact
                                                    @(_pendingReceiverForPlacement?.Id == receiver.Id ? "pdf-toolbar__btn--signature-change-active" : "")"
                                             @onclick="() => ActivatePlacementForReceiver(receiver)"
+                                            style="@(_pendingReceiverForPlacement?.Id == receiver.Id ? $"background:{receiver.Color};color:#fff;border-color:{receiver.Color};" : $"color:{receiver.Color};border-color:{receiver.Color};")"
                                             title="Signaturfeld platzieren">
                                         <svg xmlns="http://www.w3.org/2000/svg" width="14" height="14" fill="currentColor" viewBox="0 0 16 16">
                                             <path d="M12.146.146a.5.5 0 0 1 .708 0l3 3a.5.5 0 0 1 0 .708l-10 10a.5.5 0 0 1-.168.11l-5 2a.5.5 0 0 1-.65-.65l2-5a.5.5 0 0 1 .11-.168l10-10z" />
@@ -155,7 +157,7 @@
         @* Placement mode hint bar *@
         @if (_pendingReceiverForPlacement is not null)
         {
-            <div style="background: #4F46E5; color: white; font-size: 0.75rem; font-weight: 500;
+            <div style="background: @_pendingReceiverForPlacement.Color; color: white; font-size: 0.75rem; font-weight: 500;
                         padding: 0.3rem 1.5rem; text-align: center; letter-spacing: 0.01em;">
                 📌 Klicken Sie auf die Stelle im Dokument für <strong>@_pendingReceiverForPlacement.FullName</strong>.
                 &nbsp;<button @onclick="CancelPlacement"
@@ -483,7 +485,8 @@
             XPt:          xPt,
             YPt:          yPt,
             Page:         page1Based,
-            ReceiverName: _pendingReceiverForPlacement.FullName);
+            ReceiverName: _pendingReceiverForPlacement.FullName,
+            Color:        _pendingReceiverForPlacement.Color);
 
         _signatureFields.Add(field);
         _pendingReceiverForPlacement = null;
@@ -565,25 +568,6 @@
         var document = PdfSharp.Pdf.IO.PdfReader.Open(
             inputMs, PdfSharp.Pdf.IO.PdfDocumentOpenMode.Modify);
 
-        // Visual style — same palette as the receiver-side placeholder
-        var fillBrush  = new PdfSharp.Drawing.XSolidBrush(PdfSharp.Drawing.XColor.FromArgb( 40,  60,  80, 160));
-        var borderPen  = new PdfSharp.Drawing.XPen(PdfSharp.Drawing.XColor.FromArgb(200,  60,  80, 200), 1.5);
-        var textBrush  = new PdfSharp.Drawing.XSolidBrush(PdfSharp.Drawing.XColor.FromArgb(200,  40,  60, 140));
-        var nameBrush  = new PdfSharp.Drawing.XSolidBrush(PdfSharp.Drawing.XColor.FromArgb(255,  30,  30, 100));
-        var fontLabel  = new PdfSharp.Drawing.XFont("Arial",  9, PdfSharp.Drawing.XFontStyleEx.Bold);
-        var fontName   = new PdfSharp.Drawing.XFont("Arial",  7, PdfSharp.Drawing.XFontStyleEx.Regular);
-
-        var fmtCenter = new PdfSharp.Drawing.XStringFormat
-        {
-            Alignment     = PdfSharp.Drawing.XStringAlignment.Center,
-            LineAlignment = PdfSharp.Drawing.XLineAlignment.Center,
-        };
-        var fmtBottomCenter = new PdfSharp.Drawing.XStringFormat
-        {
-            Alignment     = PdfSharp.Drawing.XStringAlignment.Center,
-            LineAlignment = PdfSharp.Drawing.XLineAlignment.Far,
-        };
-
         foreach (var field in fields)
         {
             int pageIndex = field.Page - 1;
@@ -592,6 +576,21 @@
             var page = document.Pages[pageIndex];
             using var gfx = PdfSharp.Drawing.XGraphics.FromPdfPage(page);
 
+            // Derive colours from the receiver's hex colour
+            var fillBrush = new PdfSharp.Drawing.XSolidBrush(HexToXColor(field.Color, alpha: 35));
+            var borderPen = new PdfSharp.Drawing.XPen(HexToXColor(field.Color, alpha: 210), 1.5);
+            var textBrush = new PdfSharp.Drawing.XSolidBrush(HexToXColor(field.Color, alpha: 200));
+            var nameBrush = new PdfSharp.Drawing.XSolidBrush(HexToXColor(field.Color, alpha: 230));
+
+            var fontLabel = new PdfSharp.Drawing.XFont("Arial", 9, PdfSharp.Drawing.XFontStyleEx.Bold);
+            var fontName  = new PdfSharp.Drawing.XFont("Arial", 7, PdfSharp.Drawing.XFontStyleEx.Regular);
+
+            var fmtCenter = new PdfSharp.Drawing.XStringFormat
+            {
+                Alignment     = PdfSharp.Drawing.XStringAlignment.Center,
+                LineAlignment = PdfSharp.Drawing.XLineAlignment.Center,
+            };
+
             var rect = new PdfSharp.Drawing.XRect(field.XPt, field.YPt, SigWidthPt, SigHeightPt);
 
             gfx.DrawRectangle(fillBrush, rect);
@@ -616,6 +615,13 @@
         return outputMs.ToArray();
     }
 
+    /// <summary>Converts a CSS hex colour string (e.g. "#4F46E5") to a PdfSharp XColor.</summary>
+    static PdfSharp.Drawing.XColor HexToXColor(string hex, int alpha)
+    {
+        var c = System.Drawing.ColorTranslator.FromHtml(hex);
+        return PdfSharp.Drawing.XColor.FromArgb(alpha, c.R, c.G, c.B);
+    }
+
     // ── Receiver popup ──
     void OpenAddReceiverPopup()
     {
@@ -777,22 +783,36 @@
             return Task.CompletedTask;
         }
 
-        _receivers.Add(new ReceiverDraft(Guid.NewGuid(), fullName, email, phoneNumber));
+        _receivers.Add(new ReceiverDraft(Guid.NewGuid(), fullName, email, phoneNumber,
+            ReceiverPalette[_receivers.Count % ReceiverPalette.Length]));
         PersistSession();
         CloseAddReceiverPopup();
         return Task.CompletedTask;
     }
 
     // ── Models ──
-    record SignatureFieldDraft(double XPt, double YPt, int Page, string ReceiverName);
+    record SignatureFieldDraft(double XPt, double YPt, int Page, string ReceiverName, string Color);
 
     record NormalisedCoords(double NormX, double NormY, int PageIndex);
 
-    record ReceiverDraft(Guid Id, string FullName, string Email, string PhoneNumber);
+    record ReceiverDraft(Guid Id, string FullName, string Email, string PhoneNumber, string Color);
 
     record EditorSessionData(
         byte[]                   OriginalPdfBytes,
         List<SignatureFieldDraft> Fields,
         string                   FileName,
         List<ReceiverDraft>      Receivers);
+
+    // ── Receiver colour palette (cycles when > 8 receivers) ──
+    static readonly string[] ReceiverPalette =
+    [
+        "#4F46E5", // indigo
+        "#059669", // emerald
+        "#DC2626", // red
+        "#D97706", // amber
+        "#7C3AED", // violet
+        "#0891B2", // cyan
+        "#BE185D", // pink
+        "#65A30D", // lime
+    ];
 }