feat(EnvelopeCookieManager): add EnvelopeCookieManager to support envelope-specific cookie names

- Introduce EnvelopeCookieManager wrapper around ChunkingCookieManager to generate dynamic cookie names based on envelopeReceiverId or envKey. Ensures request/response cookies are scoped per envelope.

EnvelopeGenerator.Web/EnvelopeCookieManager.cs

@@ -0,0 +1,49 @@
+using Microsoft.AspNetCore.Authentication.Cookies;
+
+namespace EnvelopeGenerator.Web;
+
+public class EnvelopeCookieManager : ICookieManager
+{
+    private readonly IEnumerable<string> _envelopeKeyBasedCookieNames;
+
+    private readonly ChunkingCookieManager _inner = new();
+
+    public EnvelopeCookieManager(params string[] envelopeKeyBasedCookieNames)
+    {
+        _envelopeKeyBasedCookieNames = envelopeKeyBasedCookieNames;
+    }
+
+    private string GetCookieName(HttpContext context, string key)
+    {
+        if (!_envelopeKeyBasedCookieNames.Contains(key))
+            return key;
+
+        var envId = context.GetRouteValue("envelopeReceiverId")?.ToString();
+
+        if (string.IsNullOrEmpty(envId) && context.Request.Query.TryGetValue("envKey", out var envKeyValue))
+            envId = envKeyValue;
+
+        if (string.IsNullOrEmpty(envId))
+            return key;
+
+        return $"{key}-{envId}";
+    }
+
+    public string? GetRequestCookie(HttpContext context, string key)
+    {
+        var cookieName = GetCookieName(context, key);
+        return _inner.GetRequestCookie(context, cookieName);
+    }
+
+    public void AppendResponseCookie(HttpContext context, string key, string? value, CookieOptions options)
+    {
+        var cookieName = GetCookieName(context, key);
+        _inner.AppendResponseCookie(context, cookieName, value, options);
+    }
+
+    public void DeleteCookie(HttpContext context, string key, CookieOptions options)
+    {
+        var cookieName = GetCookieName(context, key);
+        _inner.DeleteCookie(context, cookieName, options);
+    }
+}