Refactor project structure in solution

Replaced "EnvelopeGenerator.WebUI" with "EnvelopeGenerator.Server" and "EnvelopeGenerator.WebUI.Client" with "EnvelopeGenerator.Server.Client". Updated project entries, solution configuration platforms, and nested projects to reflect these changes.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/SignatureCacheService.cs

@@ -0,0 +1,66 @@
+using System.Net.Http.Json;
+using Microsoft.Extensions.Options;
+using EnvelopeGenerator.WebUI.Client.Options;
+using EnvelopeGenerator.WebUI.Client.Models;
+
+namespace EnvelopeGenerator.WebUI.Client.Services;
+
+/// <summary>
+/// Client service for managing cached signatures via API.
+/// </summary>
+public class SignatureCacheService(HttpClient http, IOptions<ApiOptions> apiOptions)
+{
+    private readonly ApiOptions _api = apiOptions.Value;
+
+    public async Task SaveSignatureAsync(
+        string envelopeKey,
+        SignatureCaptureDto signature,
+        CancellationToken cancel = default)
+    {
+        var response = await http.PostAsJsonAsync(
+            $"{_api.BaseUrl}/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
+            signature,
+            cancel);
+
+        if (!response.IsSuccessStatusCode)
+        {
+            var error = await response.Content.ReadAsStringAsync(cancel);
+            throw new HttpRequestException($"Failed to cache signature: {response.StatusCode} - {error}");
+        }
+    }
+
+    public async Task<SignatureCaptureDto?> GetSignatureAsync(
+        string envelopeKey,
+        CancellationToken cancel = default)
+    {
+        var response = await http.GetAsync(
+            $"{_api.BaseUrl}/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
+            cancel);
+
+        if (response.StatusCode == System.Net.HttpStatusCode.NotFound)
+            return null;
+
+        if (!response.IsSuccessStatusCode)
+        {
+            var error = await response.Content.ReadAsStringAsync(cancel);
+            throw new HttpRequestException($"Failed to retrieve signature: {response.StatusCode} - {error}");
+        }
+
+        return await response.Content.ReadFromJsonAsync<SignatureCaptureDto>(cancellationToken: cancel);
+    }
+
+    public async Task DeleteSignatureAsync(
+        string envelopeKey,
+        CancellationToken cancel = default)
+    {
+        var response = await http.DeleteAsync(
+            $"{_api.BaseUrl}/api/Cache/SignatureCapture/{Uri.EscapeDataString(envelopeKey)}",
+            cancel);
+
+        if (!response.IsSuccessStatusCode)
+        {
+            var error = await response.Content.ReadAsStringAsync(cancel);
+            throw new HttpRequestException($"Failed to delete signature: {response.StatusCode} - {error}");
+        }
+    }
+}