fix(auth): reject expired JWT on session read (silent-401 shell)

readFromStorage validated token shape but never checked exp, so an expired
token mounted the full authed shell and every API call 401d silently. Decode
the JWT and treat an expired token as no session. Pattern backported from
skyai-finance. Frontend audit 2026-06-20, rank 1.

Also clears the localStorage Session in onUnauthorized (root.tsx) so a 401
fully logs out instead of leaving a dead session behind getToken.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/root.tsx

@@ -15,6 +15,7 @@ import { CommandBusProvider } from "@crema/action-bus"
 import { ArcadiaProvider } from "@crema/arcadia-client"
 import { LlmConfigBootstrap } from "~/lib/llm-config-bootstrap"
 import { ProfileBootstrap } from "~/lib/profile-bootstrap"
+import { signOut } from "~/lib/session"
 // CREMA:PROVIDERS-IMPORTS
 
 const ARCADIA_URL = import.meta.env.VITE_ARCADIA_URL ?? "http://localhost:4000"
@@ -59,6 +60,10 @@ export default function App() {
           if (typeof window !== "undefined") {
             sessionStorage.removeItem("arcadia_access_token")
             sessionStorage.removeItem("arcadia_refresh_token")
+            // Also clear the localStorage Session (crema.session); otherwise
+            // useSession() still reports "logged in" after a 401 and the shell
+            // keeps mounting with a dead token. (Frontend audit 2026-06-20.)
+            signOut()
           }
         }}
       >