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/lib/use-refresh.ts

@@ -0,0 +1,46 @@
+'use client'
+
+import { useCallback } from 'react'
+import { useQueryClient } from '@tanstack/react-query'
+import { useNoteRefresh } from '@/context/NoteRefreshContext'
+import { queryKeys, invalidateNotes, invalidateNotebooks, invalidateLabels } from './query-hooks'
+
+/**
+ * Combined refresh hook that:
+ * 1. Calls triggerRefresh() for backward compatibility (NoteRefreshContext)
+ * 2. Invalidates React Query cache for the affected keys
+ *
+ * This allows gradual migration from triggerRefresh to pure React Query.
+ */
+export function useRefresh() {
+  const queryClient = useQueryClient()
+  const { triggerRefresh, triggerNotebooksRefresh } = useNoteRefresh()
+
+  const refreshNotes = useCallback((notebookId?: string | null) => {
+    // Invalidate React Query cache
+    invalidateNotes(queryClient, notebookId)
+    // Trigger old refresh mechanism
+    triggerRefresh()
+  }, [queryClient, triggerRefresh])
+
+  const refreshNotebooks = useCallback(() => {
+    // Invalidate React Query cache
+    invalidateNotebooks(queryClient)
+    // Trigger old refresh mechanism
+    triggerNotebooksRefresh()
+  }, [queryClient, triggerNotebooksRefresh])
+
+  const refreshLabels = useCallback((notebookId?: string | null) => {
+    invalidateLabels(queryClient, notebookId)
+    triggerRefresh() // Labels affect note display too
+  }, [queryClient, triggerRefresh])
+
+  return {
+    refreshNotes,
+    refreshNotebooks,
+    refreshLabels,
+    // For direct query invalidation without triggering refresh
+    queryClient,
+    queryKeys,
+  }
+}