Revert "feat(auth-files): add external migration modal for antigravity credentials"

This reverts commit 2086c348a9.

src/i18n/locales/en.json

@@ -330,17 +330,6 @@
     "title": "Auth Files Management",
     "title_section": "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.",
-    "migrate_button": "Import from external?",
-    "migrate_title": "External Migration",
-    "migrate_subtitle": "gcli2api",
-    "migrate_email_label": "Email",
-    "migrate_email_placeholder": "Enter email to generate the credential",
-    "migrate_email_hint": "Used for the email field and the file name",
-    "migrate_email_required": "Enter an email first",
-    "migrate_upload_button": "Antigrvity Credential",
-    "migrate_parse_error": "Unable to parse credential file",
-    "migrate_missing_fields": "Credential missing required fields: {{fields}}",
-    "migrate_success": "Migration complete. Credential uploaded.",
     "upload_button": "Upload File",
     "delete_all_button": "Delete All",
     "empty_title": "No Auth Files",

src/i18n/locales/zh-CN.json

@@ -330,17 +330,6 @@
     "title": "认证文件管理",
     "title_section": "认证文件",
     "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。",
-    "migrate_button": "从外部迁移？",
-    "migrate_title": "外部迁移",
-    "migrate_subtitle": "gcli2api",
-    "migrate_email_label": "邮箱",
-    "migrate_email_placeholder": "输入邮箱用于生成认证文件",
-    "migrate_email_hint": "该邮箱将写入凭证并生成文件名",
-    "migrate_email_required": "请先填写邮箱",
-    "migrate_upload_button": "Antigrvity凭证",
-    "migrate_parse_error": "无法解析凭证文件",
-    "migrate_missing_fields": "凭证缺少必要字段: {{fields}}",
-    "migrate_success": "迁移完成，凭证已上传",
     "upload_button": "上传文件",
     "delete_all_button": "删除全部",
     "empty_title": "暂无认证文件",