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-selector.tsx

@@ -7,7 +7,7 @@ import { Badge } from '@/components/ui/badge'
 import { Input } from '@/components/ui/input'
 import { Tag, Plus, Check } from 'lucide-react'
 import { cn } from '@/lib/utils'
-import { useLabels } from '@/context/LabelContext'
+import { useNotebooks } from '@/context/notebooks-context'
 import { LabelBadge } from './label-badge'
 import { useLanguage } from '@/lib/i18n'
 
@@ -26,7 +26,7 @@ export function LabelSelector({
   triggerLabel,
   align = 'start',
 }: LabelSelectorProps) {
-  const { labels, loading, addLabel } = useLabels()
+  const { labels, isLoading: loading, addLabel } = useNotebooks()
   const { t } = useLanguage()
   const [search, setSearch] = useState('')