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

includes/i18n/zh_tw.php

@@ -85,7 +85,11 @@ $i18n = [
     'average_monthly' => "平均每月訂閱費用",
     'most_expensive'  => "最高的訂閱費用",
     'amount_due'      => "本月應付金額",
+    'percentage_budget_used' => "預算使用率",
+    'budget_remaining' => "剩餘預算",
+    'amount_over_budget' => "預算超支",
     'monthly_savings' => "每月節省",
+    'yearly_savings'  => "每年節省",
     'split_views'     => "分割檢視",
     'category_split'  => "類別分割",
     'household_split' => "家庭分割",
@@ -101,6 +105,8 @@ $i18n = [
     'upload_avatar'   => "上传头像",
     'file_type_error' => "文件类型不允许",
     'user_details'    => "使用者詳細資訊",
+    "monthly_budget"  => "每月預算",
+    "budget_info"     => "設定預算後，您可以在統計頁面上比較預算和實際支出。",
     "household"       => "家庭",
     "save_member"     => "儲存成員",
     "delete_member"   => "刪除成員",