Replace native confirm dialogs with custom styled modal

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/index.html

@@ -393,6 +393,19 @@
     </div>
 </div>
 
+<!-- 确认弹窗 -->
+<div class="paste-modal" id="confirmModal">
+    <div class="paste-modal-content" style="max-width:380px;text-align:center;">
+        <div class="paste-modal-icon" id="confirmIcon" style="margin:0 auto 1rem;"><i class="bi bi-question-circle"></i></div>
+        <h3 class="paste-modal-title" id="confirmTitle" style="margin-bottom:8px;">确认操作</h3>
+        <p class="paste-modal-subtitle" id="confirmMessage" style="margin-bottom:1.5rem;"></p>
+        <div class="paste-modal-buttons" style="justify-content:center;">
+            <button class="btn btn-cancel" id="confirmCancelBtn">取消</button>
+            <button class="btn btn-primary" id="confirmOkBtn"><i class="bi bi-check2"></i> 确定</button>
+        </div>
+    </div>
+</div>
+
 <!-- Toast 提示 -->
 <div class="toast-container" id="toastContainer"></div>