Feat/agent folder section add

[ultrahighsuper]

Related Issue

Description

The Agent Folder sidebar previously showed both folders and files under a single section labeled “Files”, which was confusing. This change adds a dedicated “Folders” section and ensures:

• Folders section contains only folders (folders-only tree view)
• Files section contains only files (flattened list, using relative paths for clarity)

Implementation:

• Updated src/components/Folder/index.tsx
  • Added filterFolderOnlyTree() to build a folders-only tree from the existing file tree.
  • Rendered two sections in the sidebar: chat.folders and chat.files.
  • Built a files-only list from fileGroups[0].files and sorted it.
• Added i18n key chat.folders across locales.

Testing Evidence (REQUIRED)

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline

[ultrahighsuper]

please check this pr and merge to main

[ultrahighsuper]

@4pmtong
Please check this PR.

[ultrahighsuper]

@Wendong-Fan
please check this PR.
It has 2 weeks pending.