feat: MVP-5 Sprint 2 - Command Palette and Global Shortcuts

- Add Command Palette (Ctrl+K / Cmd+K) with search and navigation
- Add global keyboard shortcuts: g h (dashboard), g n (notes), n (new note)
- Add keyboard shortcuts help dialog (?)
- Add shortcuts provider component
- Shortcuts ignore inputs/textareas for proper UX

src/components/keyboard-shortcuts-dialog.tsx

@@ -0,0 +1,39 @@
+'use client'
+import { Dialog, DialogContent, DialogHeader, DialogTitle } from '@/components/ui/dialog'
+import { Keyboard } from 'lucide-react'
+
+const shortcuts = [
+  { keys: ['n'], description: 'Nueva nota' },
+  { keys: ['g', 'h'], description: 'Ir al Dashboard' },
+  { keys: ['g', 'n'], description: 'Ir a Notas' },
+  { keys: ['/'], description: 'Enfocar búsqueda' },
+  { keys: ['?'], description: 'Mostrar atajos' },
+  { keys: ['Ctrl', 'K'], description: 'Command Palette' },
+]
+
+export function KeyboardShortcutsDialog({ open, onOpenChange }: { open: boolean, onOpenChange: (o: boolean) => void }) {
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent>
+        <DialogHeader>
+          <DialogTitle className="flex items-center gap-2">
+            <Keyboard className="h-5 w-5" />
+            Atajos de teclado
+          </DialogTitle>
+        </DialogHeader>
+        <div className="divide-y">
+          {shortcuts.map((s) => (
+            <div key={s.description} className="flex justify-between py-2">
+              <span className="text-sm">{s.description}</span>
+              <div className="flex gap-1">
+                {s.keys.map((k) => (
+                  <kbd key={k} className="px-2 py-1 bg-muted rounded text-xs">{k}</kbd>
+                ))}
+              </div>
+            </div>
+          ))}
+        </div>
+      </DialogContent>
+    </Dialog>
+  )
+}