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/query-provider.tsx

@@ -0,0 +1,26 @@
+'use client'
+
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { useState, type ReactNode } from 'react'
+
+export function QueryProvider({ children }: { children: ReactNode }) {
+  const [queryClient] = useState(
+    () =>
+      new QueryClient({
+        defaultOptions: {
+          queries: {
+            staleTime: 30 * 1000, // 30 seconds
+            gcTime: 5 * 60 * 1000, // 5 minutes (was cacheTime)
+            retry: 1,
+            refetchOnWindowFocus: false,
+          },
+        },
+      })
+  )
+
+  return (
+    <QueryClientProvider client={queryClient}>
+      {children}
+    </QueryClientProvider>
+  )
+}