Add MVC architecture overview

[PureWeen]

Add MVC architecture overview

• You've read the Contributor Guide and Code of Conduct.
• You've included unit or integration tests for your change, where applicable.
• You've included inline docs for your change, where applicable.
• There's an open issue for the PR that you are making. If you'd like to propose a new feature or change, please open an issue to discuss the change or find an existing issue.

Add an in-area MVC architecture reference for contributors and coding agents

Description

Context

This PR extracts durable MVC technical knowledge from the broader #69011 effort into an in-area architecture reference for contributors and coding agents only. MVC area owners can validate and merge the document independently.

The single-file src/Mvc/ARCHITECTURE.md shape follows the in-area architecture pattern established by @javiercn in #69147, with the sibling SignalR #69200 and gRPC #69216 extractions as additional examples where useful.

Summary

• add only src/Mvc/ARCHITECTURE.md as an MVC architecture overview
• document how MVC service composition, application models, action descriptors, and endpoint construction fit together
• describe controller and Razor Pages invocation, filters, model binding, validation, result execution, formatters, and view rendering
• capture dependency injection, lifetime, caching, diagnostics, Hot Reload, and trimming boundaries
• distinguish MVC-owned integration from adjacent subsystems and map focused documentation, verification boundaries, and terminology

Documentation only; no runtime or public API changes.

Validation

• git diff --check and git diff --check origin/main...HEAD passed
• all 47 relative Markdown links in src/Mvc/ARCHITECTURE.md (40 unique targets) resolve on disk; there are no local anchors
• git diff --stat origin/main...HEAD shows one new file only: src/Mvc/ARCHITECTURE.md (353 added lines)
• markdownlint was not run locally; the repository workflow targets docs/**/*.md, not this in-area document

Related to #69011; this extraction does not close the wider effort.

[Copilot]

Copilot review overview

🟢 Approval recommended

The documentation-only change is fully reviewed, and the remaining diagnostic wording issue is a minor nit that does not block approval.

Review tier: Lite
Findings: None

What changed in this PR

Adds a documentation-only MVC architecture overview covering composition, invocation pipelines, integration boundaries, and verification guidance.

Changes:

• Documents MVC services, descriptors, endpoints, binding, filters, results, and rendering.
• Clarifies ownership boundaries with adjacent subsystems.
• Captures lifetimes, caching, diagnostics, Hot Reload, and trimming considerations.

File	Review summary
src/​Mvc/​ARCHITECTURE.md	Adds the MVC architecture overview. A minor nit requests distinguishing model-binding logging from DiagnosticListener diagnostics.

---

💡 Add a code-review agent skill for context-aware, tailored reviews. Learn more in the docs.

[dotnet-policy-service]

Looks like this PR hasn't been active for some time and the codebase could have been changed in the meantime.
To make sure no conflicting changes have occurred, please rerun validation before merging. You can do this by leaving an /azp run comment here (requires commit rights), or by simply closing and reopening.

[Copilot]

Copilot review overview

🟢 Approval recommended

The documentation aligns with the current implementation and all local links resolve.

Review effort: Balanced
Findings: None