profile: bootstrap avatar URL on app boot

The appbar's <Avatar> reads avatarUrl from the localStorage profile
mirror. Without a global fetcher, that mirror only got populated when
the user navigated to /profile, so a fresh browser session showed
initials in the appbar until then.

- ProfileBootstrap component runs in root.tsx alongside
  LlmConfigBootstrap. On mount and on session change, fetches the
  arcadia profile and caches the resolved avatar URL.
- profile.tsx loadAccount now also persists the URL into localStorage
  on initial fetch (was in-memory only) so it survives reloads.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/root.tsx

@@ -14,6 +14,7 @@ import { ToastProvider, Toaster } from "@crema/notification-ui"
 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"
 // CREMA:PROVIDERS-IMPORTS
 
 const ARCADIA_URL = import.meta.env.VITE_ARCADIA_URL ?? "http://localhost:4000"
@@ -63,6 +64,7 @@ export default function App() {
       >
         <CommandBusProvider>
           <LlmConfigBootstrap />
+          <ProfileBootstrap />
           <Outlet />
           <Toaster />
         </CommandBusProvider>