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.

Cargo.toml

@@ -17,7 +17,7 @@ edition = "2021"
 tokio = { version = "1", features = ["full"] }
 axum = { version = "0.8" }
 tower = { version = "0.5" }
-tower-http = { version = "0.6", features = ["cors", "trace", "fs", "compression-gzip", "timeout"] }
+tower-http = { version = "0.6", features = ["cors", "trace", "fs", "compression-gzip", "timeout", "set-header"] }
 hyper = { version = "1" }
 bytes = "1"
 serde = { version = "1", features = ["derive"] }