feat: add monthly budget field and statistics (#329)

includes/i18n/zh_cn.php

@@ -90,7 +90,11 @@ $i18n = [
     'average_monthly' => "平均每月订阅费用",
     'most_expensive'  => "最昂贵订阅费用",
     'amount_due'      => "本月应付金额",
+    'percentage_budget_used' => "预算使用百分比",
+    'budget_remaining' => "剩余预算",
+    'amount_over_budget' => "超出预算",
     'monthly_savings' => "每月节省",
+    'yearly_savings'  => "每年节省",
     'split_views'     => "拆分视图",
     'category_split'  => "分类视图",
     'household_split' => "家庭视图",
@@ -108,6 +112,8 @@ $i18n = [
     'upload_avatar'   => "上传头像",
     'file_type_error' => "文件类型不允许",
     'user_details'    => "用户详情",
+    "monthly_budget"  => "每月预算",
+    "budget_info"     => "设置预算后，您可以在统计页面上比较预算和实际支出。",
     "household"       => "家庭",
     "save_member"     => "保存成员",
     "delete_member"   => "删除成员",