manifests: plain block scalars for sql

task_type link_prediction -> recommendation; manifests as YAML block scalars

Write task labels in canonical sorted order (row reorder only)

Write task labels in canonical sorted order (row reorder only)

restore autocomplete train/val parquets

autocomplete tasks: drop hosted train/val labels (deterministically regenerable from the db; test.parquet kept for db-free leaderboard eval)

rel-amazon: YAML manifests + descriptions + schema card

Add rel-amazon (manifest layout)