feat: support .NET 11 preview

[ArgoZhang]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

BootstrapBlazor currently targets up to .NET 10 and its build, CI, and container configuration use the .NET 10 SDK and runtime. The project cannot yet be built or tested against the .NET 11 preview APIs.

Describe the solution you'd like

Add net11.0 to the supported target frameworks and use the .NET 11 preview SDK through global.json.

Update package references, GitHub Actions, and Docker images for the .NET 11 preview. Adapt ValidateForm.ValidateAsync to the native .NET 11 EditContext.ValidateAsync API while retaining the existing implementation for earlier target frameworks, and update component tests to use asynchronous event helpers.

Additional context

The existing net6.0 through net10.0 targets remain supported.

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@ArgoZhang Thank you for contacting us. We will give feedback later.