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/en.json

@@ -344,10 +344,21 @@
     "title": "Configure Usage Query",
     "enableUsageQuery": "Enable usage query",
     "presetTemplate": "Preset template",
+    "templateCustom": "Custom",
+    "templateGeneral": "General",
+    "templateNewAPI": "NewAPI",
+    "accessToken": "Access Token",
+    "accessTokenPlaceholder": "Generate in 'Security Settings'",
+    "userId": "User ID",
+    "userIdPlaceholder": "e.g., 114514",
+    "defaultPlan": "Default Plan",
+    "queryFailedMessage": "Query failed",
     "queryScript": "Query script (JavaScript)",
     "timeoutSeconds": "Timeout (seconds)",
     "scriptHelp": "Script writing instructions:",
     "configFormat": "Configuration format:",
+    "commentOptional": "optional",
+    "commentResponseIsJson": "response is the JSON data returned by the API",
     "extractorFormat": "Extractor return format (all fields optional):",
     "tips": "💡 Tips:",
     "testing": "Testing...",