[Blazor] Add Blazor Components architecture overview (#69147)

* Add Blazor Components architecture overview

Document the Components subsystem composition, runtime models, architectural boundaries, historically grounded design principles, subsystem map, and terminology.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Expand Blazor architecture subsystem map

Include Gateway, WebAssembly Server, WebAssembly Authentication, and AI, and clarify where related extension assemblies are documented.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>