feat: MVP-5 Sprint 3 - Sidebar, Work Mode, and Drafts

- Enhance note-connections with collapsible sections and recent versions
- Add work mode toggle in header for focused work
- Add draft autosave with 7-day TTL and recovery banner
- Save drafts on changes for new notes

src/components/work-mode-toggle.tsx

@@ -0,0 +1,26 @@
+'use client'
+import { useState, useEffect } from 'react'
+import { getWorkMode, setWorkMode } from '@/lib/work-mode'
+import { Button } from '@/components/ui/button'
+import { Monitor, Eye } from 'lucide-react'
+
+export function WorkModeToggle() {
+  const [enabled, setEnabled] = useState(false)
+
+  useEffect(() => {
+    setEnabled(getWorkMode())
+  }, [])
+
+  const toggle = () => {
+    const newValue = !enabled
+    setEnabled(newValue)
+    setWorkMode(newValue)
+    // Could dispatch custom event for other components to listen
+  }
+
+  return (
+    <Button variant="ghost" size="sm" onClick={toggle} title="Modo trabajo">
+      {enabled ? <Eye className="h-4 w-4" /> : <Monitor className="h-4 w-4" />}
+    </Button>
+  )
+}