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-manager.tsx

@@ -16,7 +16,7 @@ import { Badge } from './ui/badge'
 import { Tag, X, Plus, Palette, AlertCircle } from 'lucide-react'
 import { LABEL_COLORS, LabelColorName } from '@/lib/types'
 import { cn } from '@/lib/utils'
-import { useLabels, Label } from '@/context/LabelContext'
+import { useNotebooks } from '@/context/notebooks-context'
 import { useLanguage } from '@/lib/i18n'
 
 interface LabelManagerProps {
@@ -26,7 +26,7 @@ interface LabelManagerProps {
 }
 
 export function LabelManager({ existingLabels, notebookId, onUpdate }: LabelManagerProps) {
-  const { labels, loading, addLabel, updateLabel, deleteLabel, getLabelColor } = useLabels()
+  const { labels, loading, addLabel, updateLabel, deleteLabel, getLabelColor } = useNotebooks()
   const { t } = useLanguage()
   const [open, setOpen] = useState(false)
   const [newLabel, setNewLabel] = useState('')
@@ -45,18 +45,11 @@ export function LabelManager({ existingLabels, notebookId, onUpdate }: LabelMana
 
     if (trimmed && !selectedLabels.includes(trimmed)) {
       try {
-        // NotebookId is REQUIRED for label creation (PRD R2)
-        if (!notebookId) {
-          setErrorMessage(t('labels.notebookRequired'))
-          console.error(t('labels.notebookRequired'))
-          return
-        }
-
         // Get existing label color or use random
         const existingLabel = labels.find(l => l.name === trimmed)
         const color = existingLabel?.color || (Object.keys(LABEL_COLORS) as LabelColorName[])[Math.floor(Math.random() * Object.keys(LABEL_COLORS).length)]
 
-        await addLabel(trimmed, color, notebookId)
+        await addLabel(trimmed, color)
         const updated = [...selectedLabels, trimmed]
         setSelectedLabels(updated)
         setNewLabel('')