chore: normalize tsfile dataset metadata

Restore dataset card and add timeseries modality tag

Upload README.md with huggingface_hub

Rewrite dataset card in English; add tsfile tag

Organize GiftEval TsFiles by original frequency

Copy GiftEval TsFiles into frequency directories

Refresh dataset card and viewer status

Replace with converted GiftEval subset bitbrains_rnd

Copy bitbrains_rnd from Salesforce/GiftEval

initial commit