Add media image handling and related endpoints

- Introduced `MediaImage` entity to manage images for markdown in instructions and news.
- Updated `IAppDbContext` and `AppDbContext` to include `MediaImages` DbSet.
- Implemented `DeleteMediaImageFilesAsync` method in `FactoryResetCommandHandler` to remove media images during factory reset.
- Added new API endpoints for uploading and retrieving media images, enhancing markdown support.
- Updated frontend components to utilize the new `MarkdownEditor` for image uploads in instructions and news.
- Enhanced documentation to reflect the new media handling features and API specifications.

backend/src/PnvPanel.Infrastructure/Persistence/Configurations/MediaImageConfiguration.cs

@@ -0,0 +1,20 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+using PnvPanel.Domain.Media;
+
+namespace PnvPanel.Infrastructure.Persistence.Configurations;
+
+public class MediaImageConfiguration : IEntityTypeConfiguration<MediaImage>
+{
+    public void Configure(EntityTypeBuilder<MediaImage> builder)
+    {
+        builder.ToTable("MediaImages");
+        builder.HasKey(x => x.Id);
+
+        builder.Property(x => x.FileName).IsRequired().HasMaxLength(255);
+        builder.Property(x => x.StoredFileName).IsRequired().HasMaxLength(100);
+        builder.Property(x => x.ContentType).IsRequired().HasMaxLength(100);
+
+        builder.HasIndex(x => x.StoredFileName).IsUnique();
+    }
+}