[codex] Clarify Studio WASM OIDC setup

[sfmskywalker]

Summary

• Clarifies when Studio WebAssembly hosts need Razor changes.
• Documents the required Microsoft WebAssembly authentication script in index.html.
• Calls out the AuthenticationService.init console error caused by the missing script.

Why

A user configuring OIDC hit AuthenticationService undefined in the browser and asked whether App.razor, package references, or backend changes are required.

Validation

• Ran git diff --check.
• Searched the touched docs for the new AuthenticationService.js and App.razor guidance.