Add keyboard shortcut to create a new workspace

Cmd+N (Ctrl+N off mac) navigates to the new-workspace route through a
global handler keyed on the active host. The sidebar header row surfaces
the shortcut hint on hover, replacing the redundant "+" button that
duplicated the action in the Workspaces section header.

packages/app/src/hooks/use-global-new-workspace-action.ts

@@ -0,0 +1,29 @@
+import { useCallback } from "react";
+import { router } from "expo-router";
+import { useKeyboardActionHandler } from "@/hooks/use-keyboard-action-handler";
+import type { KeyboardActionId } from "@/keyboard/keyboard-action-dispatcher";
+import { useActiveWorkspaceSelection } from "@/stores/navigation-active-workspace-store";
+import { buildHostNewWorkspaceRoute } from "@/utils/host-routes";
+
+const WORKSPACE_NEW_ACTIONS: readonly KeyboardActionId[] = ["workspace.new"];
+
+export function useGlobalNewWorkspaceAction() {
+  const selection = useActiveWorkspaceSelection();
+  const serverId = selection?.serverId ?? null;
+
+  const handle = useCallback(() => {
+    if (!serverId) {
+      return false;
+    }
+    router.navigate(buildHostNewWorkspaceRoute(serverId) as never);
+    return true;
+  }, [serverId]);
+
+  useKeyboardActionHandler({
+    handlerId: "workspace-new-global",
+    actions: WORKSPACE_NEW_ACTIONS,
+    enabled: serverId !== null,
+    priority: 0,
+    handle,
+  });
+}