profile: real avatar upload + storage form fix

- Add a digital-objects client (uploadFile: open session → PUT to
  presigned URL → complete) and a profile client (getProfile,
  updateProfile, pickAvatarUrl variant resolver).
- Wire profile.tsx avatar upload to use the real flow: validate
  image+size, upload to digital_objects tagged "avatar", PATCH
  /api/v1/profile with avatar_digital_object_id, mirror the resolved
  URL into local prefs so the existing <AvatarImage> binding keeps
  working. Show Uploading… state and an inline error banner. Clear
  detaches via avatar_digital_object_id: null.
- Fix the storage form sending the wrong field name for the local
  backend — arcadia's StorageConfig changeset requires `base_path`,
  not `path`. The 422 was silent.

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

app/lib/arcadia/storage-configs.ts

@@ -149,7 +149,9 @@ export const SECRET_FIELDS: Record<StorageBackend, readonly string[]> = {
 export const REQUIRED_FIELDS: Record<StorageBackend, readonly string[]> = {
   s3: ["bucket", "region", "access_key_id", "secret_access_key"],
   gcs: ["bucket", "service_account_json"],
-  local: ["path"],
+  // Local backend's filesystem root. Backend changeset rejects "path" — must
+  // be `base_path`. Keep this in sync with `Arcadia.Storage.Adapters.Local`.
+  local: ["base_path"],
 }
 
 export const OPTIONAL_FIELDS: Record<StorageBackend, readonly string[]> = {