Add Identity Lab Blazor sample and include it in solution

[mckaragoz]

Motivation

• Provide a new interactive Blazor "Identity Lab" playground sample that demonstrates UltimateAuth in a live UI for exploring authentication, sessions and authorization.
• Ship a capability audit to document which UltimateAuth public APIs the sample uses and which features are intentionally omitted.

Description

• Add a new samples/identity-lab/CodeBeam.UltimateAuth.IdentityLab project with Program.cs, appsettings.json, and CodeBeam.UltimateAuth.IdentityLab.csproj that wires UltimateAuth server/client, in-memory store and sample seed data.
• Add Blazor components and routing including App.razor, Routes.razor, MainLayout.razor, pages Landing.razor, Access.razor, Dashboard.razor, NotAuthorized.razor, _Imports.razor, and a theme and CSS at wwwroot/app.css to present the playground UI using MudBlazor.
• Include a CAPABILITY-AUDIT.md documenting the public API boundaries used by the Identity Lab and the design decisions for omitted features.
• Update UltimateAuth.slnx to include the new sample project so it is visible in the solution structure.

Testing

• Ran dotnet build for the new sample project (samples/identity-lab/CodeBeam.UltimateAuth.IdentityLab) and the solution structure; the build completed successfully.
• Executed the repository's automated test suite with dotnet test for the existing test projects and they completed successfully without regressions.

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Codex Task