Add Cmd+Up/Down workspace navigation

Sources/Shellraiser/App/ShellraiserApp.swift

@@ -203,6 +203,20 @@ struct WorkspaceCommands: Commands {
 
             Divider()
 
+            Button("Previous Workspace") {
+                manager.selectPreviousWorkspace()
+            }
+            .keyboardShortcut(.upArrow, modifiers: [.command])
+            .disabled(manager.workspaces.count <= 1)
+
+            Button("Next Workspace") {
+                manager.selectNextWorkspace()
+            }
+            .keyboardShortcut(.downArrow, modifiers: [.command])
+            .disabled(manager.workspaces.count <= 1)
+
+            Divider()
+
             Button("Jump to Next Completed Session") {
                 manager.jumpToNextCompletedSession()
             }

Sources/Shellraiser/Services/Workspaces/WorkspaceManager+Shortcuts.swift

@@ -56,6 +56,17 @@ extension WorkspaceManager {
             }
         }
 
+        if hasCommand, !hasOption, !hasControl, !hasShift {
+            switch event.keyCode {
+            case 126:
+                return selectPreviousWorkspace()
+            case 125:
+                return selectNextWorkspace()
+            default:
+                break
+            }
+        }
+
         guard hasCommand, !hasOption, !hasControl else { return false }
 
         guard let key = event.charactersIgnoringModifiers?.lowercased(), !key.isEmpty else {

Sources/Shellraiser/Services/Workspaces/WorkspaceManager+WorkspaceLifecycle.swift

@@ -162,6 +162,30 @@ extension WorkspaceManager {
         index > 0 && index <= workspaces.count
     }
 
+    /// Selects the workspace before the current one, wrapping to the last.
+    /// Returns true if a switch occurred.
+    @discardableResult
+    func selectPreviousWorkspace() -> Bool {
+        guard workspaces.count > 1,
+              let currentId = window.selectedWorkspaceId,
+              let currentIndex = workspaces.firstIndex(where: { $0.id == currentId }) else { return false }
+        let previousIndex = (currentIndex - 1 + workspaces.count) % workspaces.count
+        selectWorkspace(workspaces[previousIndex].id)
+        return true
+    }
+
+    /// Selects the workspace after the current one, wrapping to the first.
+    /// Returns true if a switch occurred.
+    @discardableResult
+    func selectNextWorkspace() -> Bool {
+        guard workspaces.count > 1,
+              let currentId = window.selectedWorkspaceId,
+              let currentIndex = workspaces.firstIndex(where: { $0.id == currentId }) else { return false }
+        let nextIndex = (currentIndex + 1) % workspaces.count
+        selectWorkspace(workspaces[nextIndex].id)
+        return true
+    }
+
     /// Restores first-responder focus to the selected workspace's active terminal surface.
     func restoreSelectedWorkspaceTerminalFocus() {
         guard let workspaceId = window.selectedWorkspaceId,