feat(前端): 优化表单输入框样式并重构分页组件

- 为所有管理页面和登录注册页添加统一的输入框聚焦样式
- 重构分页组件为通用实现，支持页码跳转和省略号显示
- 优化分页交互体验，减少代码重复

frontend/views/auth/register.html

@@ -96,26 +96,39 @@
             text-decoration: underline;
         }
 
+        .input-group {
+            border: 1px solid #dee2e6;
+            border-radius: 0.75rem;
+            overflow: hidden;
+            transition: border-color 0.2s, box-shadow 0.2s;
+            background-color: #fff;
+        }
+
+        .input-group:focus-within {
+            border-color: #764ba2;
+            box-shadow: 0 0 0 0.2rem rgba(118, 75, 162, 0.1);
+        }
+
         .input-group-text {
             background-color: transparent;
-            border-right: none;
+            border: none;
             color: #adb5bd;
             width: 45px;
             justify-content: center;
+            padding-left: 1rem;
         }
 
         .form-control, .form-select {
-            border-left: none;
+            border: none !important;
+            padding-left: 0.5rem;
         }
 
         .form-control:focus, .form-select:focus {
             box-shadow: none;
-            border-color: #764ba2;
         }
 
-        .form-control:focus + .input-group-text,
-        .input-group-text:focus-within {
-            border-color: #764ba2;
+        .input-group:focus-within .input-group-text i {
+            color: #764ba2;
         }
 
         #classField {