Get table change status

A table's active runs plus change watermarks for rows, columns, display preferences, and the definition, in one response.

NOT A POLLING TARGET. The grid now receives changes over the change feed (GET /tables/{table_id}/events/) and fetches this once on load for its initial active-run state. It remains useful to any client that wants a cheap point-in-time snapshot without opening a stream.

Preferences are watermarked separately from columns so a hide, pin, resize, or recolour refreshes the column list alone. A client comparing two responses must compare for inequality, never ordering: max timestamps can move backward when the newest row or column is hard-deleted (the counts catch deletes). All timestamps are server-generated; never compare them to the client clock. There is deliberately no table-existence 404: an unknown or foreign table returns empty runs and null/zero watermarks, which leaks nothing (same no-leak contract as the active-runs endpoint). The org-scoped definition read gates the row aggregate, so a foreign table ID never reaches the (potentially large) row index.