Wire native undo into menus, toolbar, and command validation

The command surface was already almost entirely platform machinery —
this card proves it and pins it. Headless probes established that
NSWindow.validateMenuItem answers enablement AND rewrites the row title
from the delegate-supplied manager, so 'Undo Move 3 Cards' flows step
phrase to Edit menu with no code of ours; under the lock the rows dim
and keep their names, the correct reading of the-stack-survives. The
toolbar twins validate through validateUserInterfaceItem, which never
touches labels — 03's static-label exception proven rather than
asserted — and their specs' enablement abstention is pinned so nobody
later adds a second, disagreeing answer. The one link a headless run
cannot close is the nil-target key-window resolution itself: standard
responder-chain behavior with none of our code in it, left as the
manual check. Base-edition 'disabled without undo' scaffolding is
reworded away — every base board has undo now. New suites cover the
trash's two doors (delete-then-undo byte-identical to Put Back's
effect), position-preserving restore of a middle card, and the
capstone: five gestures forward, five presses back to the origin
board, five forward again, the menu phrase asserted after every press.

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

KanbanPro/Edition/ProEdition.swift

@@ -23,9 +23,10 @@ import Foundation
 /// board experience, agent attribution and accessibility are shared code and stay in `Kanban/`.
 ///
 /// The type itself is a namespace, not state — the composition root that picks a
-/// `HistoryProviding` per edition arrives with the providers it chooses between (base's native
-/// stack in m8-native-undo, Pro's git stack in pro-m1), and inventing a seam here before either
-/// exists would be guessing at its shape.
+/// `HistoryProviding` per edition is `AppModel.makeHistoryProvider`, and it lives in the shared
+/// tree because base's `NativeHistoryProvider` is the shared default. Pro's override is one closure
+/// installed from here once `KanbanPro/Git/` exists (pro-m1); until then Pro runs the native stack,
+/// which is the seam working rather than a gap.
 enum ProEdition {
     /// The edition's own bundle identifier (12 ▸ Targets, ruled 2026-07-27: base keeps
     /// `dev.rzen.indie.Kanban`, Pro mints its own). Stated as a constant so the value has one