Document runtime migration creation (--add option for database update)

[Copilot]

Documents the runtime migration creation feature from dotnet/efcore#37415, which allows creating and applying migrations in a single step using Roslyn compilation at runtime.

• managing.md — New "Create and apply a migration in one step" section with CLI/PowerShell tabs and behavior notes (fallback when no pending changes)
• dotnet.md — Added --add, --output-dir, and --namespace options to dotnet ef database update reference
• powershell.md — Added -Add, -OutputDir, -Namespace parameters to Update-Database reference

dotnet ef database update InitialCreate --add
dotnet ef database update AddProducts --add --output-dir Migrations/Products --namespace MyApp.Migrations

[Copilot]

Pull request overview

Documents EF Core’s runtime migration creation feature that lets users scaffold and apply a migration in a single command invocation (via Roslyn compilation at runtime), and updates the CLI/PMC reference docs accordingly.

Changes:

• Added a new “Create and apply a migration in one step” section to migrations management docs, including examples and limitations.
• Documented new dotnet ef database update options (--add, --output-dir, --namespace, --json) in the .NET CLI reference.
• Documented new Update-Database parameters (-Add, -OutputDir, -Namespace) in the PowerShell reference.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
entity-framework/core/managing-schemas/migrations/managing.md	Adds narrative guidance and examples for creating+applying a migration in one step, plus limitations.
entity-framework/core/cli/dotnet.md	Updates dotnet ef database update reference to include --add and related options and examples.
entity-framework/core/cli/powershell.md	Updates Update-Database reference with -Add and related parameters and an example.