Builds the data layer of a C# / .NET project from docs/entity_model.md with Entity Framework Core: generates the entity classes, writes IEntityTypeConfiguration Fluent API mappings (table names, decimal precision, enum conversions, foreign keys, unique indexes, binary columns), registers them in the DbContext, and adds a native C# migration with dotnet ef migrations add. Use when the user asks to "create an EF Core migration", "add ef migration", "update the schema with ef core", "map the entities in the DbContext", "generate a db migration for .net", or mentions EF Core, DbContext, Fluent API, or dotnet ef in a Blazor .NET project.