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/lib/command-items.ts

@@ -0,0 +1,16 @@
+export interface CommandItem {
+  id: string
+  label: string
+  description?: string
+  group: 'navigation' | 'actions' | 'search' | 'recent'
+  keywords?: string[]
+  action?: () => void
+  icon?: string
+}
+
+export const commands: CommandItem[] = [
+  { id: 'nav-dashboard', label: 'Ir al Dashboard', group: 'navigation', keywords: ['home'] },
+  { id: 'nav-notes', label: 'Ir a Notas', group: 'navigation', keywords: ['all notes'] },
+  { id: 'nav-settings', label: 'Ir a Configuración', group: 'navigation', keywords: ['settings'] },
+  { id: 'action-new', label: 'Crear nueva nota', group: 'actions', keywords: ['new note', 'create'] },
+]