avatar: render immediately + survive reload

The variant pipeline is async, so right after upload all four URLs in
profile.avatar_urls are still null. The first wiring attempt called
pickAvatarUrl() which returned null, and nothing visible changed even
though the upload + PATCH succeeded.

Fixes:
- pickAvatarUrl: use the actual backend keys (small/medium/large/
  original — there's no "thumbnail").
- After upload, when no variant URL is ready, fetch the raw object
  via /api/v1/digital_objects/:id/content as a blob URL for immediate
  display. Persist that URL to localStorage so the appbar's
  useProfile() picks it up via the storage event.
- ProfileBootstrap: detect stale blob: URLs cached from previous
  sessions, clear them, and refetch a fresh blob URL when variants
  still aren't ready. Eventually the persistent variant URLs land
  and overwrite.
- Force-remount AvatarImage via key={src} in the profile page and
  appbar — base-ui's Avatar.Image keeps internal load state that
  doesn't always reset on src change.
- Diagnostic logs in fetchDigitalObjectAsBlobUrl + the upload flow
  to make next debug round one step easier (kept; cheap).

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

app/lib/arcadia/profiles.ts

@@ -52,18 +52,24 @@ export async function updateProfile(
 }
 
 /**
- * Pick the most appropriate avatar URL from a profile. Prefers a small
- * variant (thumbnail / small / medium) if available; falls back to
- * `avatar_url`, then null.
+ * Pick the most appropriate avatar URL from a profile. Backend returns
+ * `avatar_urls = {small, medium, large, original}` keyed by size. The
+ * variants are populated async after image processing completes —
+ * before that, all four are `null` and we fall back to the legacy
+ * `avatar_url` string column (which is also usually null when uploads
+ * use the digital_object pipeline).
+ *
+ * Returns null when nothing is ready; caller should fall back to
+ * fetching the raw content as a blob URL.
  */
 export function pickAvatarUrl(profile: Profile | null | undefined): string | null {
   if (!profile) return null
   const variants = profile.avatar_urls
   if (variants && typeof variants === "object") {
     return (
-      variants.thumbnail ||
       variants.small ||
       variants.medium ||
+      variants.large ||
       variants.original ||
       profile.avatar_url ||
       null