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-preview.ts

@@ -3,6 +3,25 @@ import type { Note } from '@/lib/types'
 const MD_IMG = /!\[[^\]]*\]\(([^)\s]+)\)/g
 const HTML_IMG = /<img[^>]+src=["']([^"']+)["'][^>]*>/gi
 
+/** SSR-safe HTML entity decode so excerpt text matches server and client. */
+function decodeHtmlEntities(text: string): string {
+  return text
+    .replace(/&nbsp;/gi, ' ')
+    .replace(/&amp;/g, '&')
+    .replace(/&lt;/g, '<')
+    .replace(/&gt;/g, '>')
+    .replace(/&quot;/g, '"')
+    .replace(/(?:&#0*39;|&apos;)/g, "'")
+    .replace(/&#(\d+);/g, (_, code: string) => {
+      const n = Number(code)
+      return n > 0 && n < 0x110000 ? String.fromCodePoint(n) : `&#${code};`
+    })
+    .replace(/&#x([0-9a-f]+);/gi, (_, hex: string) => {
+      const n = parseInt(hex, 16)
+      return n > 0 && n < 0x110000 ? String.fromCodePoint(n) : `&#x${hex};`
+    })
+}
+
 /**
  * Plain-text preview for list view (light markdown stripping).
  */
@@ -58,6 +77,7 @@ export function getNotePlainExcerpt(note: Note, maxLen = 240): string {
   let raw = note.content || ''
   raw = raw.replace(/!\[[^\]]*\]\([^)]+\)/g, ' ')
   raw = raw.replace(/<[^>]+>/g, ' ')
+  raw = decodeHtmlEntities(raw)
   return stripMarkdownPreview(raw, maxLen)
 }