Build per-surface context menus

The remaining rows of 11-command-nexus.md § Context menus, every entry a
twin of an existing command path, never a parallel implementation:

- Card: Open (the double-click's own openCard closure, always the clicked
  card alone), Rename (Board ▸ Rename's beginRename path), Style… and the
  quick-style recents (already present), Delete (File ▸ Delete's
  store.delete on the standard widened target — selection when the clicked
  card is a member, else the card alone).
- Lane (one menu, header and empty space): Rename and Delete join the
  existing Style…/recents/Width rows, in table order.
- Trash entries and welcome recents verified already exact against the
  table; the attachment row's menu is marked for m6 beside its command.
- File ▸ Reveal in Finder gains its board-window scope, the branch the m4
  comment deferred here: the selection's folders on either side of the
  trash boundary — enabled under every lock, inspection being a read — or
  the board root with nothing selected; a selection resolving to no
  folders disables rather than guessing.

904 unit tests.

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

Kanban/App/FutureCommands.swift

@@ -72,6 +72,14 @@ struct SaveAsTemplateCommand: View {
 // (05-card-window.md § Attachments) and of a whole-window Finder file drop. Validation will be scope
 // alone — a card window in front, the read-only lock aside — `BoardInfoCommand`'s shape for its own
 // scope-only item.
+//
+// m5-context-menus, m6-card-window: the attachment row's own context menu is a second thing this
+// milestone owes — Open, Remove (system Trash), Reveal in Finder (11-command-nexus.md ▸ Context
+// menus' Attachment row), twinning the focused section's grammar keys (Return open / ⌫ remove — 05
+// ▸ Attachments) and Reveal in Finder's attachments-focused scope, exactly the way this milestone's
+// card and lane menus twin their own grammar and menu-bar commands: no new store method, no parallel
+// implementation. There is no row view to hang a `.contextMenu` off yet, so nothing scaffolds here
+// beyond this marker.
 struct AddAttachmentCommand: View {
     var body: some View {
         FutureCommand(title: "Add Attachment…", key: "a", modifiers: [.shift, .command])