Refactor DocumentDto to use DocumentDetailsDto

Introduce a new `DocumentDetailsDto` record to encapsulate shared document metadata and elements without binary payload. Refactor `DocumentDto` to inherit from `DocumentDetailsDto`, eliminating redundant properties and improving code reuse.

Convert `DocumentDto` from a class to a record for immutability. Add a parameterized constructor to `DocumentDto` for initializing binary data alongside metadata. Update `ByteData` to use the `init` accessor.

These changes enhance maintainability, reduce duplication, and enforce immutability by leveraging C# records and inheritance.

EnvelopeGenerator.Application/Common/Dto/DocumentDetailsDto.cs

@@ -0,0 +1,27 @@
+namespace EnvelopeGenerator.Application.Common.Dto;
+
+/// <summary>
+/// Data Transfer Object representing document metadata and elements without binary payload.
+/// </summary>
+public record DocumentDetailsDto
+{
+    /// <summary>
+    /// Gets or sets the unique identifier of the document.
+    /// </summary>
+    public int Id { get; init; }
+
+    /// <summary>
+    /// Gets or sets the envelope ID to which the document belongs.
+    /// </summary>
+    public int EnvelopeId { get; init; }
+
+    /// <summary>
+    /// Gets or sets the date and time when the document was added.
+    /// </summary>
+    public DateTime AddedWhen { get; init; }
+
+    /// <summary>
+    /// Gets or sets the collection of elements associated with the document for receiver interactions, if any.
+    /// </summary>
+    public IEnumerable<DocReceiverElementDto>? Elements { get; init; }
+}