Add PhotoUpload feature for uploading photos to file storage

Adds UploadPhotoCommand/Handler/Validator and PhotoUploadRepository, invoked via MediatR by other features' commands (e.g. a future CreateBreweryPhoto) rather than exposed through its own controller. Wires the feature and IFileStorageProvider into API.Core.

web/backend/Features/Features.PhotoUpload/Commands/UploadPhoto/UploadPhotoHandler.cs

@@ -0,0 +1,40 @@
+using Domain.Entities;
+using Features.ImageUploads.Repository;
+using Infrastructure.FileUpload;
+using MediatR;
+
+namespace Features.ImageUploads.Commands.UploadPhoto;
+
+/// <summary>Handles <see cref="UploadPhotoCommand" />.</summary>
+public class UploadPhotoHandler(IFileStorageProvider fileStorageProvider, IPhotoUploadRepository photoUploadRepository)
+    : IRequestHandler<UploadPhotoCommand, Guid>
+{
+    public async Task<Guid> Handle(UploadPhotoCommand request, CancellationToken cancellationToken)
+    {
+        Guid photoId = Guid.NewGuid();
+        string key = $"{request.Key}/{photoId}";
+
+        await using Stream stream = request.File.OpenReadStream();
+
+
+        await fileStorageProvider.UploadAsync(
+            key,
+            stream,
+            request.File.ContentType,
+            cancellationToken
+        );
+
+
+        Photo photo = new()
+        {
+            Hyperlink = key,
+            UploadedById = request.UploadedById,
+        };
+
+
+        await photoUploadRepository.CreateAsync(photo,cancellationToken);
+
+
+        return photoId;
+    }
+}