IA-890 : Fix assistant table ordering: delegate sorting to backend
The assistant table was re-sorting data client-side via getComparator after receiving it from the backend. Since createdAt is returned as an array [year, month, day, ...], the comparator produced incorrect ordering, causing recently created assistants to appear in the middle of the table instead of the top.
- Remove .sort() and comparator usage from applyFilter
- Remove unused getComparator import
- Backend already handles ordering via createdAt DESC — frontend now only filters