Set or clear a tenant's meeting-recording limits

PUT body: an omitted field is left alone, an explicit null CLEARS the override.

The three states are the point. max_concurrent_bots is nullable in the database precisely so a tenant can inherit API_RECALL_MAX_CONCURRENT_BOTS_DEFAULT rather than be pinned to whatever it happened to equal on the day someone edited it — sending null puts a tenant back on the default and keeps it moving with future default changes. model_fields_set on the handler is what separates "omitted" from "explicitly null"; a plain None default cannot.

The three-layer readout: the override, the inherited default, and what the gate enforces.

An operator about to change a cap needs to know whether the number on screen is this tenant's own or the fleet default it is currently inheriting, because clearing an override and setting it to the same value look identical afterwards but behave differently the next time the default moves.