Feat: add datasource Dropbox (#11488)

### What problem does this PR solve?

Add datasource Dropbox.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

web/src/locales/en.ts

@@ -742,6 +742,10 @@ Example: https://fsn1.your-objectstorage.com`,
         'Comma-separated emails whose "My Drive" contents should be indexed (include the primary admin).',
       google_driveSharedFoldersTip:
         'Comma-separated Google Drive folder links to crawl.',
+      dropboxDescription:
+        'Connect your Dropbox to sync files and folders from a chosen account.',
+      dropboxAccessTokenTip:
+        'Generate a long-lived access token in the Dropbox App Console with files.metadata.read, files.content.read, and sharing.read scopes.',
       moodleDescription:
         'Connect to your Moodle LMS to sync course content, forums, and resources.',
       moodleUrlTip:

web/src/locales/zh.ts

@@ -722,6 +722,9 @@ General：实体和关系提取提示来自 GitHub - microsoft/graphrag：基于
         '需要索引其 “我的云端硬盘” 的邮箱，多个邮箱用逗号分隔（建议包含管理员）。',
       google_driveSharedFoldersTip:
         '需要同步的 Google Drive 文件夹链接，多个链接用逗号分隔。',
+      dropboxDescription: '连接 Dropbox，同步指定账号下的文件与文件夹。',
+      dropboxAccessTokenTip:
+        '请在 Dropbox App Console 生成 Access Token，并勾选 files.metadata.read、files.content.read、sharing.read 等必要权限。',
       jiraDescription: '接入 Jira 工作区，持续同步Issues、评论与附件。',
       jiraBaseUrlTip:
         'Jira 的 Base URL，例如：https://your-domain.atlassian.net。',