Comprehensive credentials management and SSH host system fixes

Backend improvements:
- Fix SSH host update authentication system (use effectiveAuthType)
- Support both authType and authMethod field mapping
- Prevent empty password/key from overwriting existing credentials
- Add proper credentialId support for credential-based authentication

Frontend enhancements:
- Add dedicated "Add Credential" page similar to Add Host
- Refactor credentials management with consistent Host Manager styling
- Fix credential display bug (hide keyType for password credentials)
- Enhance CredentialSelector with improved API response handling

i18n internationalization:
- Fix Admin Settings i18n issues with comprehensive translation support
- Add missing credentials.* translation keys for both English and Chinese
- Fix hardcoded key type labels (RSA, ECDSA, Ed25519) with proper translations
- Add missing placeholders and form labels

UI/UX improvements:
- Update HostManager with 4-tab structure including credential management
- Improve visual consistency across credential components
- Better error handling and user feedback
- Enhanced form validation and submission logic

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

public/locales/zh/translation.json

@@ -11,6 +11,7 @@
     "updateCredential": "更新凭据",
     "credentialName": "凭据名称",
     "credentialDescription": "描述",
+    "username": "用户名",
     "searchCredentials": "搜索凭据...",
     "selectFolder": "选择文件夹",
     "selectAuthType": "选择认证类型",
@@ -33,6 +34,32 @@
     "failedToSaveCredential": "保存凭据失败",
     "failedToFetchCredentialDetails": "获取凭据详情失败",
     "failedToFetchHostsUsing": "获取使用此凭据的主机失败",
+    "loadingCredentials": "正在加载凭据...",
+    "retry": "重试",
+    "noCredentials": "暂无凭据",
+    "noCredentialsMessage": "开始创建您的第一个SSH凭据",
+    "sshCredentials": "SSH凭据",
+    "credentialsCount": "{{count}} 个凭据",
+    "refresh": "刷新",
+    "passwordRequired": "密码为必填项",
+    "sshKeyRequired": "SSH密钥为必填项",
+    "credentialAddedSuccessfully": "凭据「{{name}}」添加成功",
+    "general": "常规",
+    "description": "描述",
+    "folder": "文件夹",
+    "tags": "标签",
+    "addTagsSpaceToAdd": "添加标签（按空格键添加）",
+    "password": "密码",
+    "key": "密钥",
+    "sshPrivateKey": "SSH私钥",
+    "upload": "上传",
+    "updateKey": "更新密钥",
+    "keyPassword": "密钥密码（可选）",
+    "keyType": "密钥类型",
+    "keyTypeRSA": "RSA",
+    "keyTypeECDSA": "ECDSA", 
+    "keyTypeEd25519": "Ed25519",
+    "updateCredential": "更新凭据",
     "basicInfo": "基本信息",
     "authentication": "认证方式",
     "organization": "组织管理",
@@ -236,6 +263,7 @@
   },
   "admin": {
     "title": "管理员设置",
+    "oidc": "OIDC",
     "users": "用户",
     "userManagement": "用户管理",
     "makeAdmin": "设为管理员",
@@ -807,6 +835,9 @@
     "hostname": "主机名",
     "folder": "文件夹",
     "password": "密码",
+    "credentialName": "我的SSH服务器",
+    "description": "SSH凭据描述",
+    "searchCredentials": "按名称、用户名或标签搜索凭据...",
     "keyPassword": "密钥密码",
     "sshConfig": "端点 SSH 配置",
     "homePath": "/home",
@@ -818,6 +849,7 @@
     "userIdField": "sub",
     "usernameField": "name",
     "scopes": "openid email profile",
+    "userinfoUrl": "https://your-provider.com/application/o/userinfo/",
     "enterUsername": "输入用户名以设为管理员",
     "searchHosts": "按名称、用户名、IP、文件夹、标签搜索主机...",
     "enterPassword": "输入您的密码",