Expand and clarify migrations guidance.

[AndriySvyryd]

Fixes #736
Fixes #1043
Fixes #2952
Fixes #3258
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Fixes #564

[Copilot]

Pull request overview

This PR expands and clarifies EF Core migrations guidance across multiple docs pages, and adds/updates samples to support the recommended workflows (separate migrations project, migration bundles, data operations in migrations, and corrected custom operation SQL generation).

Changes:

• Improve migrations documentation around team workflows, deployment strategies (scripts vs bundles vs tooling), and separate migrations projects.
• Add new samples for a migration bundle workflow and for design-time DbContext creation in a separate migrations project.
• Fix and extend sample code used in docs (e.g., custom migration operation type mapping, new data-operations snippets).

Reviewed changes

Copilot reviewed 25 out of 27 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
samples/core/Schemas/ThreeProjectMigrations/WebApplication1/WebApplication1.csproj	Simplifies reference to migrations project for the 3-project sample.
samples/core/Schemas/ThreeProjectMigrations/WebApplication1.Migrations/WebApplication1.Migrations.csproj	Adds EF design-time and provider packages to support tooling in migrations project.
samples/core/Schemas/ThreeProjectMigrations/WebApplication1.Migrations/ApplicationDbContextFactory.cs	Adds design-time factory used by docs/tools for separate migrations project.
samples/core/Schemas/ThreeProjectMigrations/WebApplication1.Data/WebApplication1.Data.csproj	Updates package versions to align with the sample’s target framework/version set.
samples/core/Schemas/Migrations/DataOperations.cs	Adds migration data-operation examples for docs snippets.
samples/core/Schemas/Migrations/CustomOperation.cs	Fixes string type mapping acquisition in custom operation sample.
samples/core/Schemas/MigrationBundle/Program.cs	Adds a small verification entrypoint for the migration bundle sample.
samples/core/Schemas/MigrationBundle/Migrations/BloggingContextModelSnapshot.cs	Adds model snapshot for the migration bundle sample.
samples/core/Schemas/MigrationBundle/Migrations/20260805232730_AddIsActive.Designer.cs	Adds generated designer for the second migration in the bundle sample.
samples/core/Schemas/MigrationBundle/Migrations/20260805232730_AddIsActive.cs	Adds the second migration in the bundle sample.
samples/core/Schemas/MigrationBundle/Migrations/20260805232705_InitialCreate.Designer.cs	Adds generated designer for the initial migration in the bundle sample.
samples/core/Schemas/MigrationBundle/Migrations/20260805232705_InitialCreate.cs	Adds the initial migration in the bundle sample.
samples/core/Schemas/MigrationBundle/MigrationBundle.csproj	Introduces a new sample project for migration bundles.
samples/core/Schemas/MigrationBundle/BloggingContextFactory.cs	Adds design-time factory for the bundle sample context.
samples/core/Schemas/MigrationBundle/BloggingContext.cs	Adds a context with seeding delegates and schema-existence checks for rollback safety.
samples/core/Schemas/MigrationBundle/Blog.cs	Adds the sample entity type.
samples/core/Samples.sln	Registers the new MigrationBundle project in the samples solution.
entity-framework/core/modeling/data-seeding.md	Clarifies seeding behavior during deployment/migrations and links to bundle/script tradeoffs.
entity-framework/core/managing-schemas/migrations/teams.md	Adds guidance for diverged migration trees and source-control rollbacks.
entity-framework/core/managing-schemas/migrations/projects.md	Rewrites/expands separate migrations project guidance with a 3-project layout and tooling commands.
entity-framework/core/managing-schemas/migrations/operations.md	Adds guidance pointing readers at built-in data operations before custom operations.
entity-framework/core/managing-schemas/migrations/managing.md	Expands “data operations” coverage and adds guidance for removal/listing/squashing scenarios.
entity-framework/core/managing-schemas/migrations/index.md	Updates overview guidance with pointers to projects/bundles/scripts and next steps.
entity-framework/core/managing-schemas/migrations/applying.md	Adds a deployment strategy matrix and expands bundle/script/environment guidance.
entity-framework/core/cli/powershell.md	Adds warning clarifying Update-Database -Migration downgrade behavior.
entity-framework/core/cli/dotnet.md	Adds warning clarifying dotnet ef database update <migration> downgrade behavior and --output note.
entity-framework/core/cli/dbcontext-creation.md	Clarifies design-time factory precedence and updates references/links.

Files not reviewed (2)

• samples/core/Schemas/MigrationBundle/Migrations/20260805232705_InitialCreate.Designer.cs: Generated file
• samples/core/Schemas/MigrationBundle/Migrations/20260805232730_AddIsActive.Designer.cs: Generated file

[Copilot]

Pull request overview

Copilot reviewed 25 out of 27 changed files in this pull request and generated no new comments.

Files not reviewed (2)

• samples/core/Schemas/MigrationBundle/Migrations/20260805232705_InitialCreate.Designer.cs: Generated file
• samples/core/Schemas/MigrationBundle/Migrations/20260805232730_AddIsActive.Designer.cs: Generated file