feat: brainstorm sessions, PDF document Q&A, embedding fixes, and UI improvements

- Add brainstorm feature with collaborative canvas, AI idea generation, live cursors, playback, and export
- Add PDF upload/extraction/ingestion pipeline with pgvector document search (RAG)
- Add document Q&A overlay with streaming chat and PDF preview
- Add note attachments UI with status polling, grid layout, and auto-scroll
- Add task extraction AI tool and agent executor improvements
- Fix NoteEmbedding missing updatedAt column, re-index 66 notes with 1536-dim embeddings
- Fix brainstorm 'Create Note' button: add success toast and redirect to created note
- Fix memory echo notification infinite polling
- Fix chat route to always include document_search tool
- Add brainstorm i18n keys across all 14 locales
- Add socket server for real-time brainstorm collaboration
- Add hierarchical notebook selector and organize notebook dialog improvements
- Add sidebar brainstorm section with session management
- Update prisma schema with brainstorm tables, attachments, and document chunks

memento-note/components/note-editor/note-editor-context.tsx

@@ -664,10 +664,10 @@ export function NoteEditorProvider({ note, readOnly = false, fullPage = false, o
       queryClient.invalidateQueries({ queryKey: queryKeys.notes(note.notebookId) })
       triggerRefresh()
       setIsDirty(false)
-      toast.success('Note sauvegardée !')
+      toast.success(t('notes.saved') || 'Saved')
     } catch (error) {
       console.error('[SAVE] updateNote failed:', error)
-      toast.error('Erreur lors de la sauvegarde.')
+      toast.error(t('notes.saveFailed') || 'Save failed')
     } finally {
       setIsSaving(false)
     }