feat: design system overhaul — sidebar, AI chats, settings, brainstorm, color cleanup

- Sidebar: dynamic brand-accent colors, brainstorm section restyled
- AI chat general: popup panel with expand/collapse, hides when contextual AI open
- AI chat contextual: tabs reordered (Actions first), X close button, height fix
- Settings: all tabs restyled, 6 new color presets (sage, terracotta, iron, etc.)
- Global color cleanup: emerald/orange hardcoded → brand-accent dynamic
- Brainstorm page: orange → brand-accent throughout
- PageEntry animation component added to key pages
- Floating AI button: bg-brand-accent instead of hardcoded black
- i18n: all 15 locales updated with new AI/billing keys
- Billing: freemium quota tracking, BYOK, stripe subscription scaffolding
- Admin: integrated into new design
- AGENTS.md + CLAUDE.md project rules added

memento-note/context/notebooks-context.tsx

@@ -21,6 +21,7 @@ export interface UpdateNotebookInput {
   name?: string
   icon?: string
   color?: string
+  parentId?: string | null
 }
 
 export interface CreateLabelInput {
@@ -56,6 +57,7 @@ export interface NotebooksContextValue {
   // Actions: Notebooks
   createNotebookOptimistic: (data: CreateNotebookInput) => Promise<void>
   updateNotebook: (notebookId: string, data: UpdateNotebookInput) => Promise<void>
+  moveNotebookToParent: (notebookId: string, parentId: string | null) => Promise<void>
   deleteNotebook: (notebookId: string) => Promise<void>
   trashNotebook: (notebookId: string) => Promise<void>
   restoreNotebook: (notebookId: string) => Promise<void>
@@ -204,6 +206,23 @@ export function NotebooksProvider({ children, initialNotebooks = [] }: Notebooks
     triggerRefresh()
   }, [queryClient, triggerNotebooksRefresh, triggerRefresh])
 
+  const moveNotebookToParent = useCallback(async (notebookId: string, parentId: string | null) => {
+    const response = await fetch(`/api/notebooks/${notebookId}`, {
+      method: 'PATCH',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ parentId }),
+    })
+
+    if (!response.ok) {
+      const data = await response.json().catch(() => ({}))
+      throw new Error(data.error || 'Failed to move notebook')
+    }
+
+    queryClient.invalidateQueries({ queryKey: queryKeys.notebooks() })
+    triggerNotebooksRefresh()
+    triggerRefresh()
+  }, [queryClient, triggerNotebooksRefresh, triggerRefresh])
+
   const deleteNotebook = useCallback(async (notebookId: string) => {
     const response = await fetch(`/api/notebooks/${notebookId}`, {
       method: 'DELETE',
@@ -426,6 +445,7 @@ export function NotebooksProvider({ children, initialNotebooks = [] }: Notebooks
     getLabelColor,
     createNotebookOptimistic,
     updateNotebook,
+    moveNotebookToParent,
     deleteNotebook,
     trashNotebook,
     restoreNotebook,
@@ -454,6 +474,7 @@ export function NotebooksProvider({ children, initialNotebooks = [] }: Notebooks
     getLabelColor,
     createNotebookOptimistic,
     updateNotebook,
+    moveNotebookToParent,
     deleteNotebook,
     trashNotebook,
     restoreNotebook,