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/lib/profile-bootstrap.tsx

@@ -0,0 +1,47 @@
+// Fetches the arcadia profile on app boot (and after login) and caches
+// the resolved avatar URL in localStorage so the appbar's <Avatar> shows
+// immediately, without waiting for the user to navigate to /profile.
+
+import { useEffect } from "react"
+import { useArcadiaClient } from "@crema/arcadia-client"
+
+import { getProfile, pickAvatarUrl } from "~/lib/arcadia/profiles"
+import { loadProfile, saveProfile } from "~/lib/profile"
+
+export function ProfileBootstrap() {
+  const arcadia = useArcadiaClient()
+
+  useEffect(() => {
+    let cancelled = false
+
+    const tryBootstrap = async () => {
+      const token =
+        typeof window !== "undefined"
+          ? sessionStorage.getItem("arcadia_access_token")
+          : null
+      if (!token) return
+      try {
+        const p = await getProfile(arcadia)
+        if (cancelled) return
+        const url = pickAvatarUrl(p)
+        if (!url) return
+        const current = loadProfile()
+        if (current.avatarUrl === url) return
+        saveProfile({ ...current, avatarUrl: url })
+      } catch {
+        // 401 / network — silently skip; will retry on next session change.
+      }
+    }
+
+    void tryBootstrap()
+
+    const onSessionChange = () => void tryBootstrap()
+    window.addEventListener("crema:session-change", onSessionChange)
+    return () => {
+      cancelled = true
+      window.removeEventListener("crema:session-change", onSessionChange)
+    }
+  }, [arcadia])
+
+  return null
+}