Unify annotation schemas (EV bcq, VQA + Temporal field union) so HF viewer can load

VANTAGE-Bench update: prompts + question-only annotations + Vantage2DPointing rename + test split + data/README + CHANGELOG

Restructure data/: drop Spatial, rename to dense_captioning / event_verification / pointing / referring / temporal_localization / vqa (#5)

Replace data/ with new 4 GB proportional subset (#3)

Add VANTAGE-Bench subset (media + annotations + MANIFEST) (#1)