strop v0.27.0

The multibuffer gets its presentation (0049 §6), and picker rows gain
structure coloring.

Added

• Collection cards: one rounded card per source file — top border
  with the path in accent, language and modified badges, excerpt bodies
  guttering their SOURCE line numbers, a ⋮ N source lines omitted gap
  row between disjoint excerpts of one file, and a full-width bottom
  border. Cards present in path order. The title row reports matches,
  files and dirty sources. Chrome rows are typed, addressable and
  protected (edits refuse and the view refreshes) — structure is data
  (CollectionRow), never parsed back from text.
• Picker locator dimming: file rows dim the directory portion and
  keep the name bright; grep/jump/remote hits dim the path:line
  locator — computed from payload fields, not text parsing.