fix: resolve all 6 prefer-const eslint errors for CI

memento-note/lib/note-preview.ts

@@ -8,7 +8,7 @@ const HTML_IMG = /<img[^>]+src=["']([^"']+)["'][^>]*>/gi
  */
 export function stripMarkdownPreview(raw: string, maxLen = 180): string {
   if (!raw?.trim()) return ''
-  let t = raw
+  const t = raw
     .replace(/^#{1,6}\s+/gm, '')
     .replace(/```[\s\S]*?```/g, ' ')
     .replace(/\*\*([^*]+)\*\*/g, '$1')