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-badge.tsx

@@ -4,7 +4,7 @@ import { Badge } from '@/components/ui/badge'
 import { X } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { LABEL_COLORS } from '@/lib/types'
-import { useLabels } from '@/context/LabelContext'
+import { useNotebooks } from '@/context/notebooks-context'
 
 interface LabelBadgeProps {
   label: string
@@ -23,7 +23,7 @@ export function LabelBadge({
   isSelected = false,
   isDisabled = false,
 }: LabelBadgeProps) {
-  const { getLabelColor } = useLabels()
+  const { getLabelColor } = useNotebooks()
   const colorName = getLabelColor(label)
   const colorClasses = LABEL_COLORS[colorName] || LABEL_COLORS.gray