Rename fixture-named result keys to sample-named keys

stage shards via bucket API instead of volume mount

fix HF Jobs polling namespace

stage shard artifacts through HF bucket

submit: stream live eval progress to the submitter's status panel

submit: retry Hub commits on 429/5xx + persistent status panel

submit: allow missing fixture outputs

submit+app: gate Submit on HF OAuth; populate hf_username from profile

submit: default validation + hf_username fields on the pending row