Records the visual-brainstorm outcome for #827's grouped view: a cluster becomes one
contained card (event/tag as header, first 5 letters + show-more), the leftover bin
collapses to a count-only drawer, derived/world fixtures stay plain, and REQ-001/003/014/020
are amended. Mockups under .superpowers/brainstorm/ (gitignored).
Refs #827#847
