APPLICATION EXTENDED - Add light query for EnvelopeReceiver status checks

Introduced ReadEnvelopeReceiverLightQuery and its handler to efficiently load only Envelope (with Histories and User) and Receiver data, omitting Documents/Elements. This is intended for status-check scenarios to improve performance by reducing unnecessary data loading.

EnvelopeGenerator.Application/EnvelopeReceivers/Queries/ReadEnvelopeReceiverLightQuery.cs

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+using AutoMapper;
+using DigitalData.Core.Abstraction.Application.Repository;
+using EnvelopeGenerator.Application.Common.Dto.EnvelopeReceiver;
+using EnvelopeGenerator.Application.Common.Extensions;
+using EnvelopeGenerator.Application.Common.Query;
+using EnvelopeGenerator.Application.Envelopes.Queries;
+using EnvelopeGenerator.Application.Receivers.Queries;
+using EnvelopeGenerator.Domain.Entities;
+using MediatR;
+using Microsoft.EntityFrameworkCore;
+
+namespace EnvelopeGenerator.Application.EnvelopeReceivers.Queries;
+
+/// <summary>
+/// Leichte Variante von <see cref="ReadEnvelopeReceiverQuery"/>:
+/// Lädt NUR Envelope (mit Histories + User) und Receiver.
+/// Lädt NICHT Documents/Elements.
+/// 
+/// Verwendung: Status-Prüfungen wo keine Dokument-Daten benötigt werden
+/// (z.B. ReceiverAuthController.GetStatus).
+/// </summary>
+public record ReadEnvelopeReceiverLightQuery
+    : EnvelopeReceiverQueryBase<ReadEnvelopeQuery, ReadReceiverQuery>, IRequest<EnvelopeReceiverDto?>;
+
+/// <summary>
+/// Handler für <see cref="ReadEnvelopeReceiverLightQuery"/>.
+/// </summary>
+public class ReadEnvelopeReceiverLightQueryHandler
+    : IRequestHandler<ReadEnvelopeReceiverLightQuery, EnvelopeReceiverDto?>
+{
+    private readonly IRepository<EnvelopeReceiver> _repo;
+    private readonly IMapper _mapper;
+
+    /// <summary>
+    /// Konstruktor.
+    /// </summary>
+    /// <param name="repo">EnvelopeReceiver-Repository</param>
+    /// <param name="mapper">AutoMapper</param>
+    public ReadEnvelopeReceiverLightQueryHandler(IRepository<EnvelopeReceiver> repo, IMapper mapper)
+    {
+        _repo = repo;
+        _mapper = mapper;
+    }
+
+    /// <summary>
+    /// Lädt einen EnvelopeReceiver ohne Documents/Elements.
+    /// </summary>
+    public async Task<EnvelopeReceiverDto?> Handle(ReadEnvelopeReceiverLightQuery request, CancellationToken cancel)
+    {
+        var envRcv = await _repo.Query
+            .Where(request, notnull: false)
+            .AsNoTracking()
+            .Include(er => er.Envelope).ThenInclude(e => e!.Histories)
+            .Include(er => er.Envelope).ThenInclude(e => e!.User)
+            .Include(er => er.Receiver)
+            .FirstOrDefaultAsync(cancel);
+
+        return envRcv is null ? null : _mapper.Map<EnvelopeReceiverDto>(envRcv);
+    }
+}