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/context/editor-ui-context.tsx

@@ -0,0 +1,74 @@
+'use client'
+
+import { createContext, useContext, useState, useCallback, useMemo, type ReactNode } from 'react'
+
+export type HomeUiControls = {
+  isTabsMode: boolean
+  openNoteComposer: () => void
+}
+
+interface EditorUIContextValue {
+  // HomeView controls
+  controls: HomeUiControls | null
+  setControls: (c: HomeUiControls | null) => void
+
+  // NotebookDrag controls
+  draggedNoteId: string | null
+  dragOverNotebookId: string | null
+  startDrag: (noteId: string) => void
+  endDrag: () => void
+  dragOver: (notebookId: string | null) => void
+  isDragging: boolean
+  isDragOver: boolean
+}
+
+const EditorUIContext = createContext<EditorUIContextValue | null>(null)
+
+export function EditorUIProvider({ children }: { children: ReactNode }) {
+  // HomeView state
+  const [controls, setControls] = useState<HomeUiControls | null>(null)
+
+  // NotebookDrag state
+  const [draggedNoteId, setDraggedNoteId] = useState<string | null>(null)
+  const [dragOverNotebookId, setDragOverNotebookId] = useState<string | null>(null)
+
+  const startDrag = useCallback((noteId: string) => {
+    setDraggedNoteId(noteId)
+  }, [])
+
+  const endDrag = useCallback(() => {
+    setDraggedNoteId(null)
+    setDragOverNotebookId(null)
+  }, [])
+
+  const dragOver = useCallback((notebookId: string | null) => {
+    setDragOverNotebookId(notebookId)
+  }, [])
+
+  const isDragging = draggedNoteId !== null
+  const isDragOver = dragOverNotebookId !== null
+
+  const value = useMemo<EditorUIContextValue>(() => ({
+    controls,
+    setControls,
+    draggedNoteId,
+    dragOverNotebookId,
+    startDrag,
+    endDrag,
+    dragOver,
+    isDragging,
+    isDragOver,
+  }), [controls, draggedNoteId, dragOverNotebookId, startDrag, endDrag, dragOver, isDragging, isDragOver])
+
+  return <EditorUIContext.Provider value={value}>{children}</EditorUIContext.Provider>
+}
+
+export function useEditorUI() {
+  const ctx = useContext(EditorUIContext)
+  if (!ctx) throw new Error('useEditorUI must be used within EditorUIProvider')
+  return ctx
+}
+
+export function useEditorUIOptional(): EditorUIContextValue | null {
+  return useContext(EditorUIContext)
+}