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-wrapper.tsx

@@ -3,7 +3,7 @@
 import { Suspense } from 'react'
 import { Header } from './header'
 import { useSearchParams, useRouter } from 'next/navigation'
-import { useLabels } from '@/context/LabelContext'
+import { useNotebooks } from '@/context/notebooks-context'
 
 interface HeaderWrapperProps {
   onColorFilterChange?: (color: string | null) => void
@@ -13,7 +13,7 @@ interface HeaderWrapperProps {
 function HeaderContent({ onColorFilterChange, user }: HeaderWrapperProps) {
   const searchParams = useSearchParams()
   const router = useRouter()
-  const { labels } = useLabels()
+  const { labels } = useNotebooks()
   
   const selectedLabels = searchParams.get('labels')?.split(',').filter(Boolean) || []
   const selectedColor = searchParams.get('color') || null