Add "Apply migrations" section to MVC validation tutorial

[Copilot]

Fixes #10429

The ASP.NET Core MVC validation tutorial (Part 9) was missing guidance on running an EF Core migration after adding validation attributes that affect the database schema — leaving the model and DB schema out of sync. The Razor Pages equivalent tutorial already had this section.

Changes

Validation tutorial (validation.md and versioned includes for 6.0–9.0)

• Added ## Apply migrations section after "Using DataType Attributes" and before "Additional resources" in validation.md (≥ aspnetcore-10.0) and validation6.md–validation9.md
• Added [Part 8, Add a new field (EF Core migrations)](xref:tutorials/first-mvc-app/new-field) link to Additional resources in all validation tutorial files, to help readers who don't follow the series sequentially find the migrations context

The new section explains that [Required] → NOT NULL and [StringLength(60)] → nvarchar(60), and provides tabbed migration commands:

• Visual Studio: incremental migration via PMC

  Add-Migration New_DataAnnotations
  Update-Database

• Visual Studio Code: delete-and-recreate (required due to SQLite ALTER TABLE limitations, consistent with Part 8)

  dotnet ef migrations add InitialCreate
  dotnet ef database update
  

New field tutorial (new-field.md and versioned includes for 6.0–8.0)

• Updated the intro line in new-field.md (aspnetcore-10.0), new-field6.md, new-field7.md, and new-field8.md to link directly to EF Core migrations docs:
  • From: [Entity Framework](/ef/core/get-started/aspnetcore/new-db) Migrations / Code First Migrations
  • To: [Entity Framework Core migrations](/ef/core/managing-schemas/migrations/)

Metadata

• Updated ms.date and added ai-usage: ai-assisted to validation.md frontmatter

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Internal previews

📄 File	🔗 Preview link
aspnetcore/tutorials/first-mvc-app/new-field.md	Part 8, add a new field to an ASP.NET Core MVC app
aspnetcore/tutorials/first-mvc-app/validation.md	[Visual Studio](https://review.learn.microsoft.com/en-us/aspnet/core/tutorials/first-mvc-app/validation?branch=pr-en-us-36817)

[wadepickett]

Approved after several corrections commited.

[wadepickett]

@copilot, these files related to this tutorial series: new-field.md, new-field8.md new-field7.md, new-field6.md. Replace this line:
In this section Entity Framework Migrations is used to:

with this line containing the updated link:
In this section Entity Framework Core migrations is used to:

[Copilot]

@copilot, these files related to this tutorial series: new-field.md, new-field8.md new-field7.md, new-field6.md. Replace this line:
In this section [Entity Framework](/ef/core/get-started/aspnetcore...

Done in bf186d1. Updated the intro line in new-field.md (aspnetcore-10.0), new-field6.md, new-field7.md, and new-field8.md to use [Entity Framework Core migrations](/ef/core/managing-schemas/migrations/) is used to:.

[wadepickett]

Closing and reopening to force new bulid.

[wadepickett]

Approved