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/command-palette.tsx

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+'use client'
+import { useState, useEffect, useCallback } from 'react'
+import { useRouter } from 'next/navigation'
+import { Dialog, DialogContent } from '@/components/ui/dialog'
+import { Input } from '@/components/ui/input'
+import { commands, CommandItem } from '@/lib/command-items'
+import { Search, FileText, Settings, Home, Plus } from 'lucide-react'
+
+export function CommandPalette() {
+  const [open, setOpen] = useState(false)
+  const [query, setQuery] = useState('')
+  const [selectedIndex, setSelectedIndex] = useState(0)
+  const router = useRouter()
+
+  // Listen for Ctrl+K / Cmd+K
+  useEffect(() => {
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if ((e.metaKey || e.ctrlKey) && e.key === 'k') {
+        e.preventDefault()
+        setOpen(true)
+      }
+    }
+    window.addEventListener('keydown', handleKeyDown)
+    return () => window.removeEventListener('keydown', handleKeyDown)
+  }, [])
+
+  // Filter commands by query
+  const filtered = commands.filter(cmd =>
+    cmd.label.toLowerCase().includes(query.toLowerCase()) ||
+    cmd.keywords?.some(k => k.includes(query.toLowerCase()))
+  )
+
+  // Keyboard navigation
+  const handleKeyDown = (e: React.KeyboardEvent) => {
+    if (e.key === 'Escape') setOpen(false)
+    if (e.key === 'ArrowDown') setSelectedIndex(i => Math.min(i + 1, filtered.length - 1))
+    if (e.key === 'ArrowUp') setSelectedIndex(i => Math.max(i - 1, 0))
+    if (e.key === 'Enter' && filtered[selectedIndex]) {
+      executeCommand(filtered[selectedIndex])
+    }
+  }
+
+  // Execute command
+  const executeCommand = (cmd: CommandItem) => {
+    router.push(cmd.id === 'action-new' ? '/new' : `/${cmd.id.split('-')[1]}`)
+    setOpen(false)
+  }
+
+  return (
+    <Dialog open={open} onOpenChange={setOpen}>
+      <DialogContent className="sm:max-w-md p-0 gap-0">
+        <div className="flex items-center border-b px-3">
+          <Search className="h-4 w-4 text-muted-foreground" />
+          <Input
+            placeholder="Buscar comandos..."
+            className="border-0 focus-visible:ring-0"
+            value={query}
+            onChange={(e) => setQuery(e.target.value)}
+            onKeyDown={handleKeyDown}
+          />
+        </div>
+        <div className="max-h-80 overflow-y-auto">
+          {filtered.map((cmd, i) => (
+            <button
+              key={cmd.id}
+              onClick={() => executeCommand(cmd)}
+              className={`w-full px-3 py-2 text-left flex items-center gap-2 ${
+                i === selectedIndex ? 'bg-muted' : 'hover:bg-muted/50'
+              }`}
+            >
+              <span className="text-sm">{cmd.label}</span>
+              <span className="text-xs text-muted-foreground ml-auto">{cmd.group}</span>
+            </button>
+          ))}
+        </div>
+      </DialogContent>
+    </Dialog>
+  )
+}

src/components/keyboard-shortcuts-dialog.tsx

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+'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>
+  )
+}

src/components/shortcuts-provider.tsx

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+'use client'
+
+import { useGlobalShortcuts } from '@/hooks/use-global-shortcuts'
+import { KeyboardShortcutsDialog } from '@/components/keyboard-shortcuts-dialog'
+
+export function ShortcutsProvider() {
+  const { showHelp, setShowHelp } = useGlobalShortcuts()
+
+  return (
+    <KeyboardShortcutsDialog open={showHelp} onOpenChange={setShowHelp} />
+  )
+}