Add object search endpoint, hide internal metadata keys, fix toast/template bugs

- Implement missing /ui/buckets/{bucket}/objects/search route used by the
  Objects tab filter; previously returned 404 and showed 'Search failed'.
- Filter __checksum_*__ and __size__ sentinels from the object metadata
  panel so users no longer see internal keys in the UI.
- Include a body field in bucket-delete flash message so the toast shows
  distinct title and body.
- Replace Tera boolean 'or' operator with if/else fallback in
  replication_wizard.html, sites.html, iam.html.

crates/myfsio-server/templates/iam.html

@@ -31,7 +31,7 @@
 {% if iam_locked %}
 <div class="alert alert-warning" role="alert">
   <div class="fw-semibold mb-1">Administrator permissions required</div>
-  <p class="mb-0">You need the <code>iam:list_users</code> action to edit users or policies. {{ locked_reason or "Sign in with an admin identity to continue." }}</p>
+  <p class="mb-0">You need the <code>iam:list_users</code> action to edit users or policies. {% if locked_reason %}{{ locked_reason }}{% else %}Sign in with an admin identity to continue.{% endif %}</p>
 </div>
 {% endif %}