Implement the hybrid clipboard with deferred cut

⌘X/⌘C/⌘V for cards and lanes per 04-interactions.md § Clipboard:

- ClipboardStore stages full folder snapshots eagerly at the gesture into
  Application Support (at most the current copy; sweep at launch and on
  each copy purges what the pasteboard no longer references; a copy made
  before quitting pastes whole after restart) and writes the pasteboard a
  JSON manifest — every entry embedding its index.md, lane entries their
  cards' too — plus plain-text titles.
- Cut is Finder-style deferred: items dim in place off pendingCut, void on
  pasteboard takeover (changeCount, no timers), source-board close, or
  per-item external tombstoning; the first armed paste moves the surviving
  originals whole (tombstoned interior cards land in the destination's
  trash), a second paste materializes copies from staging.
- Paste anchors by the shared flatten-order rule (NewCardTarget's anchor,
  extracted); a tombstoned selection never anchors; lane paste reaches the
  right end and stays enabled on a zero-lane board; paste into the source
  board is the within-board lane duplicate; copies keep created, take
  fresh GUIDs, and strip tombstoned cards; trash-sourced copies strip
  deleted: at materialization; ⌘X is disabled on the trash side.
- A degraded paste is loud, never silent: staging gone → the embedded
  index.md fallback lands content-intact, attachments absent, and a
  BannerCenter-phrased row names what was lost.
- The standard Edit items validate through conditionally-attached
  onCommand handlers, so AppKit's enablement mirrors the availability
  predicates; text fields keep their own clipboard while focused.

879 unit tests (68 new).

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/UI/Board/TrashLaneView.swift

@@ -257,7 +257,13 @@ private struct TrashEntryRow: View {
         rowFace
             // The row being dragged out dims in place — the source stays visible in the trash,
             // because a restore is not a removal until the write lands.
-            .opacity(drops.session.isDragging(entry.id) ? 0.45 : 1)
+            .opacity(drops.session.isDragging(entry.id) ? ClipboardTreatment.dimmedOpacity : 1)
+            // The deferred cut wears the same dim wherever it lands, so the treatment is stated for
+            // every surface a `pendingCut` could name rather than for two of the three. In practice
+            // it never fires here: ⌘X is disabled on tombstoned selections (04-interactions.md ▸ The
+            // trash), and a pending cut is homogeneous by liveness — a reload that tombstones a cut
+            // card *ejects* it from the set rather than moving it to the other side.
+            .cutTreatment(of: entry.id, in: store)
             .contentShape(Rectangle())
             .onTapGesture { select() }
             .marqueeTarget(entry.id, kind: entry.isLaneEntry ? .lane : .card, side: .trashed, in: registry)