fix: remove unused Layers import breaking Docker build

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bndct-devops

frontend/src/pages/BookDetailPage.tsx

@@ -2,7 +2,7 @@ import { useEffect, useRef, useState } from 'react'
 import { useParams, useNavigate, Link } from 'react-router-dom'
 import {
   BookOpen, Camera, Download, Edit2, Save, X,
-  Calendar, Globe, Hash, Building2, AlignLeft, Layers, FileText, Trash2, Loader2,
+  Calendar, Globe, Hash, Building2, AlignLeft, FileText, Trash2, Loader2,
   Sparkles, Library, Check, BookMarked, ChevronLeft, ChevronRight,
   Tag as TagIcon
 } from 'lucide-react'