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/LaneView.swift

@@ -27,8 +27,8 @@ import SwiftUI
 /// ### What is still a later card's
 ///
 /// The search-aware filtering behind the count belongs to a later milestone. The card face is real
-/// (`CardFaceView`); what it still owes is the cut treatment and the sole-selected card's attachment
-/// carousel.
+/// (`CardFaceView`) and wears the deferred cut's dim (`cutTreatment`); what it still owes is the
+/// sole-selected card's attachment carousel.
 struct LaneView: View {
 
     let store: BoardStore
@@ -97,6 +97,9 @@ struct LaneView: View {
         }
         .background(selectionBackground)
         .overlay(selectionStroke)
+        // The deferred cut's dim (04-interactions.md ▸ Clipboard) — on the whole lane, because a cut
+        // lane is cut cards and all.
+        .cutTreatment(of: lane.id, in: store)
         .onGeometryChange(for: CGFloat.self) { $0.size.height } action: { measuredHeight = $0 }
         // **This lane's drop target**, on the whole body. It accepts *every* session type and routes
         // internally — card sessions against this lane's masonry zones, lane sessions forwarded to
@@ -746,6 +749,9 @@ private struct CardFaceView: View {
                     lineWidth: isFileHovered ? 2.5 : 1.5
                 )
         )
+        // The deferred cut's dim (04-interactions.md ▸ Clipboard: "cut items dim in place until paste
+        // moves them"). Above `contentShape` so the face stays fully clickable while it waits.
+        .cutTreatment(of: card.id, in: store)
         .contentShape(Rectangle())
         // **Clicking never edits** (04-interactions.md ▸ Selection, a pivot from the pathfinder's
         // two-stage Finder rename): one click selects and that is all it does — no timer, no