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/LiveStore/BannerCenter.swift

@@ -458,6 +458,8 @@ public final class BannerCenter {
             // looking at — which is what makes "Couldn't rename 'Fix login'" (02's own example
             // sentence) identify the right row rather than a name that never landed.
             if let title { "Couldn't rename '\(title)'" } else { "Couldn't rename the item" }
+        case let .duplicateBoard(title):
+            if let title { "Couldn't duplicate '\(title)'" } else { "Couldn't duplicate the board" }
         case let .importAttachment(filename):
             "Couldn't import '\(filename)'"
         case .listAttachments: