[APIView] Add agents.md and other documents

[tjprescott]

See: #14833

• Adds AGENTS.md to improve agentic operations
• Adds documentation on various topics that are useful for developers or agents working in the code base.

[Copilot]

Pull request overview

Adds agent-friendly, repository-local documentation for APIView to reduce reliance on external wikis and to help both developers and automation understand key architecture and operational workflows.

Changes:

• Added AGENTS.md files for APIView subprojects (root, APIViewWeb, ClientSPA, APIViewUnitTests) with build/run commands and conventions.
• Added APIView docs covering architecture overview, legacy Razor/flat-token system boundaries, release approval & CI gating flow, and sandboxing/pipeline-based review generation.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/dotnet/APIView/docs/sandboxing.md	Documents legacy “sandboxing” (pipeline-based) review generation, configuration, and limitations.
src/dotnet/APIView/docs/release_approval.md	Explains approval levels and how CI/CD gates releases using APIView status endpoints.
src/dotnet/APIView/docs/overview.md	High-level architecture overview of APIView backend/frontend, storage, token model, and diffing.
src/dotnet/APIView/docs/legacy.md	Describes legacy Razor Pages/flat-token pipeline and migration path to SPA/tree tokens.
src/dotnet/APIView/ClientSPA/AGENTS.md	Agent guidelines and common commands for the Angular SPA.
src/dotnet/APIView/APIViewWeb/AGENTS.md	Agent guidelines and conventions for the ASP.NET Core backend.
src/dotnet/APIView/APIViewUnitTests/AGENTS.md	Agent guidelines for xUnit test patterns and helpers.
src/dotnet/APIView/AGENTS.md	Root APIView agent guide linking to the new docs and key rules.

[praveenkuttappan]

Great work adding all these details to support the agent about APIView. We can use this to generate a complete guide about APIView by agent.

[AlitzelMendez]

This is a little bit confusing

yes there are two workflows, on in where the .whl/.nuget is shared and the other in where it is not

for the one that it is not (the most common scenario) the process is

Build artifact -> Build JSON token file (with the language parser in the CI, in their own step) -> /autoreview/craete

for the other one I think this diagram is perfect :) but it is the less common and I want to make very clear that the parser is not being call from apiview in most cases :)

so at least in this section we should document both workflows with something like

1. An Azure SDK CI/CD pipeline builds a package and POSTs the binary artifact to APIView.
2. An Azure SDK CI/CD pipeline with language parser generates code file token and publish to artifacts
3. APIView is called with the token file ..... The token file is stored in Azure Blob Storage; metadata goes to Azure Cosmos DB.
4. Reviewers open the review in the Angular SPA, where they can diff versions, leave comments, and approve.
5. The CI pipeline queries back for approval status (HTTP 200 = approved, 201 = namespace-approved, 202 = pending).