A picture off the pasteboard becomes a card's file, its hero, or the board's backdrop

⌘V grows an image-data branch, below the app's own clipboard format and refused
outright while a file URL is on the pasteboard: a screenshot or a browser's Copy
Image lands as "Pasted Image.png" in the anchor card's attachments/, through the
very import path Finder file drops and ⇧⌘A take — one bracket, one Finder-style
collision ladder, one set of banners, and the same silence a drop's arrival has.
A card window's ⌘V pastes onto its own card; a focused text field still wins the
selector natively. A file-shaped flavor travels byte for byte, PNG preferred when
several are offered; TIFF and BMP are re-encoded to PNG, being interchange
encodings rather than files anyone wants in a folder.

The hero key gets the setter it was born owing: "Set as Hero" on any image row of
the attachment list, "Remove Hero" on the row that holds it, with menu-bar twins
so the context entry is nobody's only home. It writes as a restyle — one key, one
bracket, one invertible step on the window's own stack — and replaces rather than
refusing, because a card has one hero and the row that has it says Remove instead.

Edit ▸ Paste as Board Background is the same payload's other destination, taking
the existing background.image convention at its word: the picture into the board
folder as "Pasted Background.png", the colour subkey untouched, the generator's
overwrite-our-own-name rule inherited and its echo memo taught to tell the two
producers apart.

Claude-Session: https://claude.ai/code/session_014PtZdPwqZuqEDLc6wZMtEy

KanbanTests/CardAttachmentsTests.swift

@@ -248,7 +248,7 @@ struct AddAttachmentTargetTests {
         let store = try BoardStore(rootURL: fixture.root)
 
         let attachments = CardAttachments()
-        CardWindowHost.configureAttachments(attachments, store: store, cardID: card1)
+        CardWindowHost.configureAttachments(attachments, store: store, cardID: card1, undo: CardWindowUndo())
         attachments.importFiles?([shot])
 
         #expect(try fixture.data("\(Ident.lane1)/\(Ident.card1)/attachments/shot.png") == Data([0x89, 0x50]))
@@ -266,7 +266,7 @@ struct AddAttachmentTargetTests {
         let store = try BoardStore(rootURL: fixture.root)
 
         let attachments = CardAttachments()
-        CardWindowHost.configureAttachments(attachments, store: store, cardID: card1)
+        CardWindowHost.configureAttachments(attachments, store: store, cardID: card1, undo: CardWindowUndo())
         attachments.removeFile?(doomed)
 
         #expect(try fixture.entryNames("\(Ident.lane1)/\(Ident.card1)/attachments").isEmpty)
@@ -285,7 +285,7 @@ struct AddAttachmentTargetTests {
         let store = try BoardStore(rootURL: fixture.root)
 
         let attachments = CardAttachments()
-        CardWindowHost.configureAttachments(attachments, store: store, cardID: card1)
+        CardWindowHost.configureAttachments(attachments, store: store, cardID: card1, undo: CardWindowUndo())
         attachments.cardFolder = cardFolder(fixture)
         attachments.names = ["shot.png"]