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/editor/smart-paste-extension.ts

@@ -0,0 +1,39 @@
+import { Extension } from '@tiptap/core'
+import type { EditorView } from '@tiptap/pm/view'
+import { Plugin, PluginKey } from '@tiptap/pm/state'
+
+export type SmartPasteHandler = (view: EditorView, event: ClipboardEvent) => boolean
+
+export const smartPastePluginKey = new PluginKey('smartPaste')
+
+declare module '@tiptap/core' {
+  interface Storage {
+    smartPaste: {
+      onPaste: SmartPasteHandler | null
+    }
+  }
+}
+
+export const SmartPasteExtension = Extension.create({
+  name: 'smartPaste',
+
+  addStorage() {
+    return {
+      onPaste: null as SmartPasteHandler | null,
+    }
+  },
+
+  addProseMirrorPlugins() {
+    const storage = this.storage
+    return [
+      new Plugin({
+        key: smartPastePluginKey,
+        props: {
+          handlePaste(view, event) {
+            return storage.onPaste?.(view, event) ?? false
+          },
+        },
+      }),
+    ]
+  },
+})