Document breaking changes: EF tools .NET Framework support and Design dependency (EF Core 9/11)

[Copilot]

Documents breaking changes from dotnet/efcore#37837 / dotnet/efcore#37745:

• EF tools no longer support .NET Framework projects (Low impact, added to EF Core 9.0 breaking changes): The actual break occurred in EF Core 9.0 — tools worked with .NET Framework in 8.0 but stopped in 9.0. Added entry to ef-core-9.0/breaking-changes.md documenting the break and mitigation (update project to target .NET).
• EF tools packages no longer reference Microsoft.EntityFrameworkCore.Design (Low impact, EF Core 11.0): The Microsoft.EntityFrameworkCore.Tools and Microsoft.EntityFrameworkCore.Tasks packages no longer have a dependency on Microsoft.EntityFrameworkCore.Design. Added entry to ef-core-11.0/breaking-changes.md with mitigation to add a direct PackageReference to Microsoft.EntityFrameworkCore.Design.
• Fixed heading levels in EF Core 11.0 breaking changes to match established convention (## for impact sections, ### for titles, #### for subsections).

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[Copilot]

Pull request overview

Updates the EF Core 11 breaking-changes documentation to capture recent EF tooling-related breaking changes, including clearer behavior around .NET Framework startup projects and the removal of a transitive Microsoft.EntityFrameworkCore.Design dependency from tools packages.

Changes:

• Adds two new “Low” impact entries to the breaking-changes Summary table.
• Introduces a new “Low-impact changes” section documenting the two EF tools breaking changes, including rationale and mitigations.

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[roji]

Not too sure about the .NET Framework breaking change note - either it's not a breaking change or it may need to be reworded (at least that's how I understood it). But otherwise LGTM.