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/label-management-dialog.tsx

@@ -14,7 +14,7 @@ import {
 import { Settings, Plus, Palette, Trash2, Tag } from 'lucide-react'
 import { LABEL_COLORS, LabelColorName } from '@/lib/types'
 import { cn } from '@/lib/utils'
-import { useLabels } from '@/context/LabelContext'
+import { useNotebooks } from '@/context/notebooks-context'
 import { useLanguage } from '@/lib/i18n'
 import { useNoteRefresh } from '@/context/NoteRefreshContext'
 
@@ -26,7 +26,7 @@ export interface LabelManagementDialogProps {
 
 export function LabelManagementDialog(props: LabelManagementDialogProps = {}) {
   const { open, onOpenChange } = props
-  const { labels, loading, addLabel, updateLabel, deleteLabel } = useLabels()
+  const { labels, isLoading: loading, addLabel, updateLabel, deleteLabel } = useNotebooks()
   const { t, language } = useLanguage()
   const { triggerRefresh } = useNoteRefresh()
   const [confirmDeleteId, setConfirmDeleteId] = useState<string | null>(null)