refactor: split NoteEditor into focused components + consolidate contexts

Phase 1: NoteEditor Split (64KB → 9 focused components)
- components/note-editor/: types.ts, context, toolbar, title-block,
  content-area, metadata-section, full-page, dialog compositions
- Maintains backwards compatibility via re-export from note-editor.tsx

Phase 2: Context Consolidation (5 → 3 contexts)
- NotebooksContext absorbs LabelContext (labels CRUD)
- EditorUIContext merges HomeViewContext + NotebookDragContext
- Removed: LabelContext, home-view-context, notebook-drag-context

Phase 3: React Query Infrastructure
- Added QueryProvider with @tanstack/react-query
- lib/query-keys.ts: centralized query key definitions
- lib/query-hooks.ts: useNotes, useNotebooksQuery, useLabelsQuery
- lib/use-refresh.ts: hybrid invalidateQueries + triggerRefresh helper
- NotebooksContext: invalidateQueries on mutations (with triggerRefresh fallback)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/components/header.tsx

@@ -21,7 +21,7 @@ import { Menu, Search, StickyNote, Tag, Moon, Sun, X, Bell, Sparkles, Grid3x3, S
 import Link from 'next/link'
 import { usePathname, useRouter, useSearchParams } from 'next/navigation'
 import { cn } from '@/lib/utils'
-import { useLabels } from '@/context/LabelContext'
+import { useNotebooks } from '@/context/notebooks-context'
 import { LabelFilter } from './label-filter'
 import { NotificationPanel } from './notification-panel'
 import { updateTheme } from '@/app/actions/profile'
@@ -53,7 +53,7 @@ export function Header({
   const pathname = usePathname()
   const router = useRouter()
   const searchParams = useSearchParams()
-  const { labels, setNotebookId } = useLabels()
+  const { labels, setNotebookId } = useNotebooks()
   const { t } = useLanguage()
   const { data: session } = useSession()