Add "+" menu button to horizontal tab bar for new terminal/browser tabs (#48)

Adds a "+" button to the tab bar (next to split buttons) that shows a
dropdown menu with "New Terminal ⌘T" and "New Browser ⌘⇧L" options.

- Uses native NSButton + NSMenu so the icon matches the split buttons
- Menu appears below the button
- Routes tab creation through new didRequestNewTab delegate method

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Sources/Workspace.swift

@@ -1443,6 +1443,17 @@ extension Workspace: BonsplitDelegate {
         }
     }
 
+    func splitTabBar(_ controller: BonsplitController, didRequestNewTab kind: String, inPane pane: PaneID) {
+        switch kind {
+        case "terminal":
+            _ = newTerminalSurface(inPane: pane)
+        case "browser":
+            _ = newBrowserSurface(inPane: pane)
+        default:
+            _ = newTerminalSurface(inPane: pane)
+        }
+    }
+
     func splitTabBar(_ controller: BonsplitController, didChangeGeometry snapshot: LayoutSnapshot) {
         _ = snapshot
         scheduleTerminalGeometryReconcile()

vendor/bonsplit

@@ -1 +1 @@
-Subproject commit 1d41e7b9ecfd310e6d780c2d93e74a34d759edc8
+Subproject commit 2ff740da4aa150202afac7e224001807c321ed7c