Build the welcome screen

The welcome window becomes the real thing: Xcode-style, hidden title
bar with background drag, branding and actions left, recents right —
rows carrying the board symbol, name, location, and the registry's
cached lane/card counts (stamped at close, never a scan at welcome
time), sorted by last opened. Launch failures surface row-level per
02: a failure joins its recents row as a warning caption, an
unresolvable bookmark renders unavailable with Forget its one
affordance, and only a failure with no row to carry it falls back to
a compact list; a board opening again heals its row. New Board
(Opt-Cmd-N) opens the Pages-style template chooser — shipped with
the single Basic template and the m9 seams marked — flowing through
the save panel into createBoard/createLane and straight into a board
window. Open Recent gains its submenu with Clear Menu (byte-identical
to forgetting every row, pinned by test), and File > Duplicate forks
the frontmost board to a Finder-style copy sibling: pending work
flushes first through the close flush's step two alone (sessions stay
open — 09's stated exception), every GUID and tombstone carries (the
whole-board carve-out from copies-remint), and the copy opens in its
own window while the original stays put. 36 new tests.

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

Kanban/Storage/BoardWriter.swift

@@ -1192,6 +1192,13 @@ public enum WriteOperation: Sendable, Equatable, CustomStringConvertible {
     /// the edit — `updateIndex` enriches it off the document it just read — which is the name the
     /// user is still looking at when the banner appears.
     case rename(title: String?)
+
+    /// File ▸ Duplicate — the whole-board copy (03-board-ui.md § Welcome screen & templates). Its
+    /// own case rather than a fold into `.copy`, on `.rename`'s reasoning: the user pressed
+    /// *Duplicate*, and a banner telling them the app could not "copy the item" would name neither
+    /// the command nor the thing. `title` is the board's display name.
+    case duplicateBoard(title: String?)
+
     case importAttachment(filename: String)
     case listAttachments
     case renumberChildren           // order-maintenance sweep (compaction)
@@ -1218,6 +1225,7 @@ public enum WriteOperation: Sendable, Equatable, CustomStringConvertible {
         case .style: .style(title: title)
         case .resize: .resize(title: title)
         case .rename: .rename(title: title)
+        case .duplicateBoard: .duplicateBoard(title: title)
         }
     }
 
@@ -1241,6 +1249,7 @@ public enum WriteOperation: Sendable, Equatable, CustomStringConvertible {
         case let .style(title): Self.phrase("style", title)
         case let .resize(title): Self.phrase("resize", title)
         case let .rename(title): Self.phrase("rename", title)
+        case let .duplicateBoard(title): Self.phrase("duplicate board", title)
         case let .importAttachment(filename): "import attachment '\(filename)'"
         case .listAttachments: "list attachments"
         case .renumberChildren: "renumber children"