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

KanbanTests/BoardRegistryTests.swift

@@ -226,6 +226,76 @@ struct BoardRegistryTests {
         #expect(registry.recents().isEmpty)
     }
 
+    // MARK: Clear Menu
+
+    @Test("Clear Menu empties the registry, and persists")
+    func forgetAllEmptiesTheRegistry() async throws {
+        let storage = try RegistryStorage()
+        defer { storage.tearDown() }
+        let first = try makeBoard()
+        defer { first.tearDown() }
+        let second = try makeBoard()
+        defer { second.tearDown() }
+
+        let registry = BoardRegistry(storageURL: storage.url)
+        registry.recordOpen(of: first.root, displayName: "First")
+        registry.recordOpen(of: second.root, displayName: "Second")
+        #expect(registry.recents().count == 2)
+
+        registry.forgetAll()
+
+        #expect(registry.recents().isEmpty)
+        #expect(BoardRegistry(storageURL: storage.url).recents().isEmpty, "Clear Menu persists")
+    }
+
+    /// The equivalence 11-command-nexus.md's Clear Menu rests on: Finder clears a *menu*, and here
+    /// the registry **is** the menu — so clearing it can only mean forgetting every record, and must
+    /// leave the file in precisely the state that forgetting them one at a time would.
+    @Test("Clear Menu is Forget applied to every row — same result, same file")
+    func forgetAllMatchesForgettingEachRow() async throws {
+        let wholesale = try RegistryStorage()
+        defer { wholesale.tearDown() }
+        let piecemeal = try RegistryStorage()
+        defer { piecemeal.tearDown() }
+        let first = try makeBoard()
+        defer { first.tearDown() }
+        let second = try makeBoard()
+        defer { second.tearDown() }
+
+        func populate(_ storage: RegistryStorage) -> BoardRegistry {
+            let registry = BoardRegistry(storageURL: storage.url)
+            registry.recordOpen(of: first.root, displayName: "First")
+            registry.recordOpen(of: second.root, displayName: "Second")
+            return registry
+        }
+
+        let bulk = populate(wholesale)
+        bulk.forgetAll()
+
+        let oneByOne = populate(piecemeal)
+        for row in oneByOne.recents() {
+            oneByOne.forget(id: row.record.id)
+        }
+
+        #expect(bulk.recents().isEmpty)
+        #expect(oneByOne.recents().isEmpty)
+        #expect(
+            try Data(contentsOf: wholesale.url) == Data(contentsOf: piecemeal.url),
+            "the two paths leave byte-identical files — there is no state Clear Menu skips"
+        )
+    }
+
+    @Test("Clear Menu on an empty registry writes nothing")
+    func forgetAllOnEmptyRegistryIsANoOp() async throws {
+        let storage = try RegistryStorage()
+        defer { storage.tearDown() }
+
+        let registry = BoardRegistry(storageURL: storage.url)
+        registry.forgetAll()
+
+        #expect(try storage.entryNames().isEmpty, "an empty registry has nothing to clear and no file to write")
+    }
+
     // MARK: Persistence
 
     @Test("Every mutation survives a reload of the file, dates included")