List Parent Tables

List distinct parent tables linking TO this table via any link column.

Used by the frontend's sub-table panel to render "Open in parent" affordances. Each result is one {parent_table_id, name, col_id, col_name} tuple; a single parent table with two link columns pointing at this one shows up twice (once per column).

Visibility: the caller must be able to see THIS table (same check as GET /bitables/{id}). Parent tables the caller can't see are filtered out so a shared child doesn't leak parent identities.