feat(frontend): add Cmd+K command palette and keyboard shortcuts (#1230)

* feat(frontend): add Cmd+K command palette and keyboard shortcuts

Wire up the existing shadcn/ui Command component as a global command
palette. Adds a useGlobalShortcuts hook for Cmd+K (palette), Cmd+Shift+N
(new chat), Cmd+, (settings), and Cmd+/ (shortcuts help overlay).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(frontend): address Copilot review feedback on command palette

- Normalize event.key with toLowerCase() for reliable Shift+key matching
- Replace dead deerflow:open-settings event with router.push navigation
- Use platform-appropriate Shift label (Shift+ on Windows/Linux, glyph on Mac)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

frontend/src/app/workspace/layout.tsx

@@ -5,6 +5,7 @@ import { useCallback, useEffect, useLayoutEffect, useState } from "react";
 import { Toaster } from "sonner";
 
 import { SidebarInset, SidebarProvider } from "@/components/ui/sidebar";
+import { CommandPalette } from "@/components/workspace/command-palette";
 import { WorkspaceSidebar } from "@/components/workspace/workspace-sidebar";
 import { getLocalSettings, useLocalSettings } from "@/core/settings";
 
@@ -39,6 +40,7 @@ export default function WorkspaceLayout({
         <WorkspaceSidebar />
         <SidebarInset className="min-w-0">{children}</SidebarInset>
       </SidebarProvider>
+      <CommandPalette />
       <Toaster position="top-center" />
     </QueryClientProvider>
   );