Record-Set Family Grouping — internal lineage vs. external-variant families in the Record Collector sidebar

The Record Collector sidebar lists every record set as a peer, which makes a tracker uploaded as v4 / v5 / v6 / v7 / v8 look like five unrelated CSVs and an in-app promotion chain look the same as a fresh upload. Two distinct family signals deserve first-class representation: the **internal-lineage family** (already in the data model via `promoted_from`) and the **external-variant family** (not modeled — separate uploads the user explicitly groups, or whose filenames share a stem). This spec defines the field, the grouping mechanism, the sidebar rendering, and the interaction with [[Enhanced-Records-List-and-Promotion-Checkpoint]] and the new two-CTA `Augment this Set` panel.