Refactor AuthenticatedState to store displayName and uid

The AuthenticatedState interface was updated to directly store the
`displayName` and `uid` properties. Previously, it stored the entire
`CasContent` object, which contained these properties along with others
that were not consistently used. This change simplifies the interface
and reduces redundancy.

routes/(apps)/students/partials/index.tsx

@@ -8,13 +8,7 @@ import SelfPortrait from "$root/routes/(apps)/students/(_components)/SelfPortrai
 
 // deno-lint-ignore require-await
 export async function Index(_request: Request, context: FreshContext<State>) {
-  return (
-    <>
-      <h2>Welcome {context.state.session?.givenName}!</h2>
-      <h3>Your amU identity</h3>
-      <SelfPortrait self={context.state.session!} />
-    </>
-  );
+  return <h2>Welcome {context.state.displayName || 'Guest'}!</h2>;
 }
 
 export const config = getPartialsConfig();