Build the attachments sidebar section

The card's complete file inventory: compact QuickLook-thumbnail rows
over Card.attachments — no reference tracking, subfolders tolerated
and unsurfaced — with a quiet header add affordance and the drop hint
empty state. The whole window is the file-drop surface, Edit mode
included (the editor's drag types were already filtered; now tested),
sharing the board's folder-refusal semantics literally: FinderDrop
moved verbatim into its own file so both windows run the same
partition and loss row. Dragged text still lands at the caret and is
inert elsewhere — the window delegate accepts file payloads only.
Rows open on double-click or Return, drag out their file URL, and
Remove is a bracketed write through FileManager.trashItem — the system
Trash, never a hard delete, returning the in-Trash URL so the promise
is testable; the attachment listing is the guard, so traversal and
subfolder names refuse in one line. Keyboard-native per 05: the
section is one Tab stop, arrows walk rows by name, Space toggles the
shared QuickLook panel, Backspace removes. File > Add Attachment
(shift-cmd-A) comes alive through the same import path.

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

Kanban/LiveStore/BannerCenter.swift

@@ -631,6 +631,13 @@ public final class BannerCenter {
             "Couldn't import '\(filename)'"
         case .listAttachments:
             "Couldn't read this card's attachments"
+        case let .removeAttachment(filename):
+            // **Finder's phrasing, deliberately** — and the one place in this app that is allowed
+            // it. The naming constraint above reserves "move to the Trash" for the *system* Trash,
+            // and this is the operation that uses it: the file really did go (or fail to go) where
+            // Finder's own ⌘⌫ sends things, so saying anything else — "remove", "delete" — would
+            // describe the board's quasi-lane instead and promise the wrong recovery.
+            "Couldn't move '\(filename)' to the Trash"
         case .renumberChildren:
             "Couldn't renumber cards"
         case let .relocateLooseFile(filename):