13.3 - EF Migration doc should be updated to use the new EF Core hosting integration

[afscrome]

13.3 introduced a new EF Hosting integration, but https://aspire.dev/integrations/databases/efcore/migrations/ is still telling you to manually run dotnet ef.

This doc should be updated to use the new hosting integration.

[IEvangelist]

Triage → @Copilot

Page: https://aspire.dev/integrations/databases/efcore/migrations/ → src/frontend/src/content/docs/integrations/databases/efcore/migrations.mdx

Scope: 13.3 introduced the new EF Core hosting integration. The migrations page still tells users to manually run dotnet ef as a separate step. Rewrite so the AppHost-driven flow via the new EF Core hosting integration is the primary path. Keep a short "Manual dotnet ef workflow" section as a fallback for users not using the hosting integration.

Acceptance

• Primary flow uses the new Aspire.Hosting.EntityFrameworkCore integration (confirm exact APIs and package id from microsoft/aspire 13.3 sources before writing examples).
• Manual dotnet ef content is preserved but demoted to a secondary section.
• Cross-link from / to [13.3] Document Aspire.Hosting.EntityFrameworkCore #536 (Document Aspire.Hosting.EntityFrameworkCore) if that work is in flight.
• No unrelated edits.