Search an LCA database for processes, product systems or flows. The database is the one named by `engine`, else this connection's default. `kind` scopes to processes, systems, flows, or `all` (all three in parallel). `query='*'` (or an empty string) enumerates everything of the given `kind` — e.g. `kind='system', query='*'` lists every product system in the database (one page of `limit`, plus the true total). With `kind='flow'`, `flow_type` (`elementary` / `product` / `waste`) filters the results; with `kind='process'`, `process_type` (`unit_process` / `system_process`) does. Returns typed refs (`p1`, `e1`, `f1`; a system hit is an `e<N>` engine-catalog ref, not a workspace `s<N>`) that stay valid for the session and are accepted by `engine_get` and `lca_run_assessment`. `scope_ref` (any engine ref such as `p3`/`e1`/`m2` from an earlier result) searches the database that ref came from instead, for comparing across databases; refs minted that way stay bound to that database.