Implement the motion language

One named home for every curve and duration — the two-voice split 03
fixes (snappy structural: drag reflow 0.18, delete 0.25, lane resize
0.2; smooth content-reflow 0.28), the scale-and-fade appear/disappear
transitions (cards 0.8, lanes 0.9), and a Reduce Motion variant on
every accessor (animations go instant, transitions go crossfade). A
post-migration grep holds the invariant: zero motion literals outside
Motion.swift. The animate-vs-snap split lands where Lanework's
one-way flow puts it: the store's reload seam. An app-mediated echo
applies its snapshot inside the structural transaction; foreign and
reconciling reloads — and every bracket-ending wholesale reload —
assign bare, because live-reload is the board becoming what's on
disk, not an event to perform. A window that merged foreign events
into an app-mediated span animates, deliberately: the ratified merge
rule makes it indistinguishable from a pure echo, and a test pins
that reading so a future mixed case fails loudly. The lane-reorder
reflow keys on the drop proposal alone (pointer tracking stays 1:1),
the resize session freezes its Reduce Motion answer at drag start so
the unit tick and the window resize can never disagree, and the m5
drag / m5 search / m7 undo voices are named seams waiting for their
call sites. 13 new tests.

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

Kanban/UI/Board/TrashCommands.swift

@@ -208,9 +208,25 @@ struct ShowTrashCommand: View {
             get: { store?.transient.isTrashVisible ?? false },
             set: { shown in
                 guard let store else { return }
-                store.transient.isTrashVisible = shown
-                if !shown, store.selection.liveness == .trashed {
-                    store.clearSelection()
+                // The re-divide is a *user-initiated structural change* — every lane compresses or
+                // relaxes as the trash's one unit joins or leaves the division — so it animates in
+                // the structural voice (03-board-ui.md § Motion; § Trash makes Show/Hide Trash "a
+                // re-divide trigger", a lane add's behaviour exactly). It is also one of the few
+                // structural changes that never touches disk, which is why it wears its own
+                // transaction here instead of arriving through the reload seam like the rest.
+                //
+                // Reduce Motion read from AppKit rather than from `@Environment`: a menu command's
+                // content is built outside any rendered hierarchy, where the environment's
+                // accessibility values are not reliably populated (`Motion.prefersReducedMotion`).
+                withAnimation(Motion.structural(reduced: Motion.prefersReducedMotion)) {
+                    store.transient.isTrashVisible = shown
+                    // Dropped inside the same transaction: the rows it pointed at are leaving under
+                    // this very animation, and a selection that cleared outside it would be the
+                    // highlight easing on its own — which 03 § Motion rules out ("the selection
+                    // highlight rides whatever transaction is active").
+                    if !shown, store.selection.liveness == .trashed {
+                        store.clearSelection()
+                    }
                 }
             }
         )