feat: editor improvements and architectural grid prototype

Multiple feature additions and improvements across the application:

- NextGen Editor: drag handles, smart paste, block actions
- Structured views: Kanban and table layouts for notes
- Architectural Grid: new brainstorming/agent interface prototype
- Flashcards: SM-2 revision algorithm with AI generation
- MCP server: robustness improvements
- Graph/PDF chat: fix click propagation and copy behavior
- Various UI/UX enhancements and bug fixes

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

memento-note/lib/note-peek-sync.ts

@@ -0,0 +1,18 @@
+/** Ouvre la note source en aperçu split (panneau gauche) sans changer d’onglet. */
+export const NOTE_PEEK_OPEN_EVENT = 'memento-note-peek-open'
+export const NOTE_PEEK_CLOSE_EVENT = 'memento-note-peek-close'
+
+export type NotePeekOpenDetail = {
+  noteId: string
+  blockId?: string
+}
+
+export function openNotePeek(detail: NotePeekOpenDetail) {
+  if (typeof window === 'undefined') return
+  window.dispatchEvent(new CustomEvent(NOTE_PEEK_OPEN_EVENT, { detail }))
+}
+
+export function closeNotePeek() {
+  if (typeof window === 'undefined') return
+  window.dispatchEvent(new CustomEvent(NOTE_PEEK_CLOSE_EVENT))
+}