fix: 修复 admin 后台分页等样式丢失问题

- admin/base.html 加载 Django admin CSS (base/changelists/forms/responsive)

- registration/base.html 加载 Django admin CSS (base/forms/login)

- jazzmin/css/main.css 添加 Django admin CSS 变量映射到 Bootstrap 5

- 新增分页/表格/按钮/搜索/过滤器等 Bootstrap 兼容样式

- admin.py list_per_page 50->20

backend/meals/admin.py

@@ -20,7 +20,7 @@ class CuisineAdmin(admin.ModelAdmin):
     list_editable = ('sort_order', 'is_active')
     list_filter = ('is_active',)
     search_fields = ('name',)
-    list_per_page = 50
+    list_per_page = 20
     actions = [activate_cuisines, deactivate_cuisines]
 
     @admin.display(description='菜品数')
@@ -45,7 +45,7 @@ class DishAdmin(admin.ModelAdmin):
     list_filter = ('dish_type', 'cuisine', 'is_active')
     search_fields = ('name', 'ingredient_detail', 'cuisine__name', 'pinyin')
     list_editable = ('ingredient_detail', 'protein', 'fat', 'calorie', 'is_active')
-    list_per_page = 50
+    list_per_page = 20
     actions = [activate_dishes, deactivate_dishes]
     fieldsets = (
         (None, {'fields': ('name', 'dish_type', 'cuisine', 'is_active')}),