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/note-input.tsx

@@ -51,7 +51,6 @@ import { GhostTags } from './ghost-tags'
 import { TitleSuggestions } from './title-suggestions'
 import { CollaboratorDialog } from './collaborator-dialog'
 import { AIAssistantActionBar } from './ai-assistant-action-bar'
-import { useLabels } from '@/context/LabelContext'
 import { useSession } from 'next-auth/react'
 import { useSearchParams } from 'next/navigation'
 import { useLanguage } from '@/lib/i18n'
@@ -106,7 +105,7 @@ export function NoteInput({
   forceExpanded = false,
   fullWidth = false,
 }: NoteInputProps) {
-  const { labels: globalLabels, addLabel } = useLabels()
+  const { labels: globalLabels, addLabel } = useNotebooks()
   const { data: session } = useSession()
   const [aiAssistantEnabled, setAiAssistantEnabled] = useState(true)
   const [autoLabelingEnabled, setAutoLabelingEnabled] = useState(true)