Add Blazor Components architecture overview

[javiercn]

Summary

• document how the major Blazor Components subsystems compose across supported runtime models
• describe architectural layers, cross-cutting boundaries, and historically grounded design principles
• map runtime subsystems to their planned focused architecture documents
• provide contributor navigation and shared terminology

The focused subsystem ARCHITECTURE.md documents will be added incrementally in follow-up changes.

[Copilot]

🟡 Changes recommended

The architecture map currently points to focused ARCHITECTURE.md files that aren’t present yet, which creates broken/unclear navigation in the new documentation.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds a top-level architecture overview for Blazor Components (src/Components) to give contributors a shared mental model of subsystem responsibilities, layering, runtime compositions, and cross-cutting boundaries across SSR, Interactive Server, Interactive WebAssembly, Auto, and Hybrid/WebView.

Changes:

• Introduces a new src/Components/ARCHITECTURE.md covering architectural layers, runtime compositions, and cross-cutting boundaries.
• Adds mermaid diagrams (composition + sequence diagrams per hosting model) to visualize dependency direction and runtime communication.
• Adds an “Architecture Documentation Map” and “Finding the Right Subsystem” lookup table to guide contributors to the right ownership boundaries.

File summaries

File	Description
src/Components/ARCHITECTURE.md	New top-level Blazor Components architecture overview, including diagrams, principles, and a subsystem navigation map.

Review details

Suppressed comments (2)

src/Components/ARCHITECTURE.md:334

• These Architecture entries refer to focused ARCHITECTURE.md files that don’t exist yet (currently only src/Components/ARCHITECTURE.md exists). Consider using a placeholder like TBD here until the follow-up documents are added, then replace with links.

| Endpoints | ASP.NET Core endpoints, static SSR, prerendering, streaming rendering, forms, and render-mode activation | `Endpoints/ARCHITECTURE.md` |
| Server | Interactive Server circuits, server renderers, reconnection, and browser transport | `Server/ARCHITECTURE.md` |
| WebAssembly | Browser-hosted .NET startup, rendering, and application execution | `WebAssembly/WebAssembly/ARCHITECTURE.md` |
| WebView | Native-process component execution and embedded web-view rendering | `WebView/WebView/ARCHITECTURE.md` |

src/Components/ARCHITECTURE.md:345

• Like the sections above, these Architecture entries point to focused ARCHITECTURE.md files that aren’t present yet. Marking them as TBD until the docs are added would make it clearer that these are planned follow-ups.

| Authorization | Authentication-state propagation and authorization components | `Authorization/ARCHITECTURE.md` |
| Forms | Form coordination, editing state, validation, and input components | `Forms/ARCHITECTURE.md` |
| QuickGrid | Data-grid composition, virtualization, sorting, and data-provider integration | `QuickGrid/Microsoft.AspNetCore.Components.QuickGrid/ARCHITECTURE.md` |
| Custom Elements | Exposing components through the browser custom-elements model | `CustomElements/ARCHITECTURE.md` |

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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