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/app/(main)/brainstorm/page.tsx

@@ -0,0 +1,14 @@
+import { Suspense } from 'react'
+import { BrainstormPage } from '@/components/brainstorm/brainstorm-page'
+
+export default function BrainstormRoute() {
+  return (
+    <Suspense fallback={
+      <div className="flex items-center justify-center h-full">
+        <div className="animate-spin h-8 w-8 border-2 border-foreground/20 border-t-foreground rounded-full" />
+      </div>
+    }>
+      <BrainstormPage />
+    </Suspense>
+  )
+}