feat(frontend): 支持批量编辑和管理已保存登录凭证

为连接表单补充已保存登录凭证的校验与提交流程，
允许新增、批量新增、测试连接时优先使用凭证

在连接列表中新增登录凭证管理入口，并支持批量编辑
时按连接类型筛选和应用已保存凭证

补充中英日文案，并修复 SSH 密钥选择器的绑定兼容性

packages/frontend/src/locales/en-US.json

@@ -215,6 +215,8 @@
       "title": "Batch Edit Connections",
       "editSelected": "Edit Selected",
       "noChange":"No change",
+      "savedCredentialMixedType": "Select only one connection type before applying a saved credential in batch.",
+      "savedCredentialTypeHint": "Batch apply works only for the same connection type",
       "selectedItems":"{count} items selected",
       "deleteSelectedButton": "Delete Selected",
       "deleteSelectedTooltip": "Delete selected connections",
@@ -273,6 +275,23 @@
       "connectionModeProxy": "Proxy Server",
       "connectionModeJumpHost": "Jump Host",
       "connectionType": "Connection Type:",
+      "credentialSource": "Credential Source",
+      "credentialSourceDirect": "Account / Password / Key",
+      "credentialSourceSaved": "Use Saved Credential",
+      "savedLoginCredential": "Login Credential",
+      "selectLoginCredential": "Select a saved credential",
+      "manageLoginCredentials": "Manage Login Credentials",
+      "savedCredentialHint": "Saved credentials take priority during test and connect. You can switch back to direct input anytime.",
+      "loginCredentialManager": "Login Credentials",
+      "addLoginCredential": "Add Login Credential",
+      "editLoginCredential": "Edit Login Credential",
+      "noLoginCredentials": "No saved login credentials yet",
+      "clearSavedCredential": "Clear saved credential",
+      "errorLoginCredentialRequired": "Please select a saved login credential.",
+      "errorCredentialRequiredFields": "Name and username are required.",
+      "errorCredentialDetails": "Failed to load login credential details.",
+      "confirmDeleteCredential": "Delete login credential {name}?",
+      "errorDeleteCredential": "Failed to delete login credential.",
       "typeSsh": "SSH",
       "typeRdp": "RDP",
       "typeVnc": "VNC",