feat(i18n): complete internationalization for usage query feature

Fully internationalized the usage query feature to support both Chinese and English.

Frontend changes:
- Refactored UsageScriptModal to use i18n translation keys
- Replaced hardcoded Chinese template names with constants
- Implemented dynamic template generation with i18n support
- Internationalized all labels, placeholders, and code comments
- Added template name mapping for translation

Backend changes:
- Replaced all hardcoded Chinese error messages in usage_script.rs
- Converted 33 error instances from AppError::Message to AppError::localized
- Added bilingual error messages for runtime, parsing, HTTP, and validation errors

Translation updates:
- Added 11 new translation key pairs to zh.json and en.json
- Covered template names, field labels, placeholders, and code comments

Impact:
- 100% i18n coverage for usage query functionality
- All user-facing text and error messages now support language switching
- Better user experience for English-speaking users

src/i18n/locales/zh.json

@@ -344,10 +344,21 @@
     "title": "配置用量查询",
     "enableUsageQuery": "启用用量查询",
     "presetTemplate": "预设模板",
+    "templateCustom": "自定义",
+    "templateGeneral": "通用模板",
+    "templateNewAPI": "NewAPI",
+    "accessToken": "访问令牌",
+    "accessTokenPlaceholder": "在'安全设置'里生成",
+    "userId": "用户 ID",
+    "userIdPlaceholder": "例如：114514",
+    "defaultPlan": "默认套餐",
+    "queryFailedMessage": "查询失败",
     "queryScript": "查询脚本（JavaScript）",
     "timeoutSeconds": "超时时间（秒）",
     "scriptHelp": "脚本编写说明：",
     "configFormat": "配置格式：",
+    "commentOptional": "可选",
+    "commentResponseIsJson": "response 是 API 返回的 JSON 数据",
     "extractorFormat": "extractor 返回格式（所有字段均为可选）：",
     "tips": "💡 提示：",
     "testing": "测试中...",