feat(app.js, i18n, index.html, styles): implement Vertex AI credential import feature

- Added functionality for importing Vertex AI credentials, including file selection and upload handling in the CLIProxyManager.
- Updated UI components in index.html to support the new Vertex AI credential import feature.
- Enhanced internationalization strings to provide appropriate labels and messages for the Vertex AI import functionality in both English and Chinese.
- Introduced new styles for the Vertex AI credential import section to ensure a consistent user experience.

i18n.js

@@ -217,7 +217,7 @@ const i18n = {
             // 认证文件管理
             'auth_files.title': '认证文件管理',
             'auth_files.title_section': '认证文件',
-            'auth_files.description': '这里管理 Qwen 和 Gemini 的认证配置文件。上传 JSON 格式的认证文件以启用相应的 AI 服务。',
+            'auth_files.description': '这里集中管理 CLI Proxy 支持的所有 JSON 认证文件（如 Qwen、Gemini、Vertex 等），上传后即可在运行时启用相应的 AI 服务。',
             'auth_files.upload_button': '上传文件',
             'auth_files.delete_all_button': '删除全部',
             'auth_files.empty_title': '暂无认证文件',
@@ -246,6 +246,7 @@ const i18n = {
             'auth_files.filter_claude': 'Claude',
             'auth_files.filter_codex': 'Codex',
             'auth_files.filter_iflow': 'iFlow',
+            'auth_files.filter_vertex': 'Vertex',
             'auth_files.filter_empty': '空文件',
             'auth_files.filter_unknown': '其他',
             'auth_files.type_qwen': 'Qwen',
@@ -255,8 +256,26 @@ const i18n = {
             'auth_files.type_claude': 'Claude',
             'auth_files.type_codex': 'Codex',
             'auth_files.type_iflow': 'iFlow',
+            'auth_files.type_vertex': 'Vertex',
             'auth_files.type_empty': '空文件',
             'auth_files.type_unknown': '其他',
+            'vertex_import.title': 'Vertex AI 凭证导入',
+            'vertex_import.description': '上传 Google 服务账号 JSON，使用 CLI vertex-import 同步规则写入 auth-dir/vertex-<project>.json。',
+            'vertex_import.location_label': '目标区域 (可选)',
+            'vertex_import.location_placeholder': 'us-central1',
+            'vertex_import.location_hint': '留空表示使用默认区域 us-central1。',
+            'vertex_import.file_label': '服务账号密钥 JSON',
+            'vertex_import.file_hint': '仅支持 Google Cloud service account key JSON 文件，私钥会自动规范化。',
+            'vertex_import.file_placeholder': '尚未选择文件',
+            'vertex_import.choose_file': '选择文件',
+            'vertex_import.import_button': '导入 Vertex 凭证',
+            'vertex_import.file_required': '请先选择 .json 凭证文件',
+            'vertex_import.success': 'Vertex 凭证导入成功',
+            'vertex_import.result_title': '凭证已保存',
+            'vertex_import.result_project': '项目 ID',
+            'vertex_import.result_email': '服务账号',
+            'vertex_import.result_location': '区域',
+            'vertex_import.result_file': '存储文件',
 
 
             // Codex OAuth
@@ -685,7 +704,7 @@ const i18n = {
             // Auth files management
             'auth_files.title': 'Auth Files Management',
             'auth_files.title_section': 'Auth Files',
-            'auth_files.description': 'Here you can manage authentication configuration files for Qwen and Gemini. Upload JSON format authentication files to enable the corresponding AI services.',
+            'auth_files.description': 'Manage all CLI Proxy JSON auth files here (e.g. Qwen, Gemini, Vertex). Uploading a credential immediately enables the corresponding AI integration.',
             'auth_files.upload_button': 'Upload File',
             'auth_files.delete_all_button': 'Delete All',
             'auth_files.empty_title': 'No Auth Files',
@@ -714,6 +733,7 @@ const i18n = {
             'auth_files.filter_claude': 'Claude',
             'auth_files.filter_codex': 'Codex',
             'auth_files.filter_iflow': 'iFlow',
+            'auth_files.filter_vertex': 'Vertex',
             'auth_files.filter_empty': 'Empty',
             'auth_files.filter_unknown': 'Other',
             'auth_files.type_qwen': 'Qwen',
@@ -723,8 +743,26 @@ const i18n = {
             'auth_files.type_claude': 'Claude',
             'auth_files.type_codex': 'Codex',
             'auth_files.type_iflow': 'iFlow',
+            'auth_files.type_vertex': 'Vertex',
             'auth_files.type_empty': 'Empty',
             'auth_files.type_unknown': 'Other',
+            'vertex_import.title': 'Vertex AI Credential Import',
+            'vertex_import.description': 'Upload a Google service account JSON to store it as auth-dir/vertex-<project>.json using the same rules as the CLI vertex-import helper.',
+            'vertex_import.location_label': 'Region (optional)',
+            'vertex_import.location_placeholder': 'us-central1',
+            'vertex_import.location_hint': 'Leave empty to use the default region us-central1.',
+            'vertex_import.file_label': 'Service account key JSON',
+            'vertex_import.file_hint': 'Only Google Cloud service account key JSON files are accepted.',
+            'vertex_import.file_placeholder': 'No file selected',
+            'vertex_import.choose_file': 'Choose File',
+            'vertex_import.import_button': 'Import Vertex Credential',
+            'vertex_import.file_required': 'Select a .json credential file first',
+            'vertex_import.success': 'Vertex credential imported successfully',
+            'vertex_import.result_title': 'Credential saved',
+            'vertex_import.result_project': 'Project ID',
+            'vertex_import.result_email': 'Service account',
+            'vertex_import.result_location': 'Region',
+            'vertex_import.result_file': 'Persisted file',
 
             // Codex OAuth
             'auth_login.codex_oauth_title': 'Codex OAuth',