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/en/translation.json

@@ -10,7 +10,8 @@
     "deleteCredential": "Delete Credential",
     "updateCredential": "Update Credential",
     "credentialName": "Credential Name",
-    "credentialDescription": "Description",
+    "credentialDescription": "Description", 
+    "username": "Username",
     "searchCredentials": "Search credentials...",
     "selectFolder": "Select Folder",
     "selectAuthType": "Select Auth Type",
@@ -33,6 +34,32 @@
     "failedToSaveCredential": "Failed to save credential",
     "failedToFetchCredentialDetails": "Failed to fetch credential details",
     "failedToFetchHostsUsing": "Failed to fetch hosts using this credential",
+    "loadingCredentials": "Loading credentials...",
+    "retry": "Retry",
+    "noCredentials": "No Credentials",
+    "noCredentialsMessage": "Start by creating your first SSH credential",
+    "sshCredentials": "SSH Credentials",
+    "credentialsCount": "{{count}} credentials",
+    "refresh": "Refresh",
+    "passwordRequired": "Password is required",
+    "sshKeyRequired": "SSH key is required", 
+    "credentialAddedSuccessfully": "Credential \"{{name}}\" added successfully",
+    "general": "General",
+    "description": "Description",
+    "folder": "Folder",
+    "tags": "Tags",
+    "addTagsSpaceToAdd": "Add tags (press space to add)",
+    "password": "Password",
+    "key": "Key",
+    "sshPrivateKey": "SSH Private Key",
+    "upload": "Upload",
+    "updateKey": "Update Key",
+    "keyPassword": "Key Password (optional)",
+    "keyType": "Key Type",
+    "keyTypeRSA": "RSA",
+    "keyTypeECDSA": "ECDSA", 
+    "keyTypeEd25519": "Ed25519",
+    "updateCredential": "Update Credential",
     "basicInfo": "Basic Info",
     "authentication": "Authentication",
     "organization": "Organization",
@@ -236,6 +263,7 @@
   },
   "admin": {
     "title": "Admin Settings",
+    "oidc": "OIDC",
     "users": "Users",
     "userManagement": "User Management",
     "makeAdmin": "Make Admin",
@@ -770,6 +798,9 @@
     "folder": "folder",
     "password": "password",
     "keyPassword": "key password",
+    "credentialName": "My SSH Server",
+    "description": "SSH credential description",
+    "searchCredentials": "Search credentials by name, username, or tags...",
     "sshConfig": "endpoint ssh configuration",
     "homePath": "/home",
     "clientId": "your-client-id",
@@ -780,6 +811,7 @@
     "userIdField": "sub",
     "usernameField": "name",
     "scopes": "openid email profile",
+    "userinfoUrl": "https://your-provider.com/application/o/userinfo/",
     "enterUsername": "Enter username to make admin",
     "searchHosts": "Search hosts by name, username, IP, folder, tags...",
     "enterPassword": "Enter your password",