[VFolder] Admin data page shows A→B folder sharing as admin's own invitation

## Summary

When an admin views the data page, a VFolder share created by user A inviting user B appears as "admin's invitation" instead of showing the actual inviter (user A).

## Reproduction Environment

- Environment: dogbowl / development environment
- Account: admin

## Reproduction Steps

1. Log in as regular user A
1. Invite user B to folder X (create a share)
1. Log in as admin
1. Navigate to the data page → shared folder list

## Expected Behavior

Admin's data page should show the A→B share record correctly, i.e., "User A shared with User B".

## Actual Behavior

The A→B share record appears as "admin's invitation" — the admin account is incorrectly shown as the inviter.

## Root Cause Hypothesis

The VFolder sharing list API likely returns incorrect inviter information when called in admin context. The admin's session identity may be incorrectly substituted as the inviter field.

## WebUI Impact

- Related issue: FR-2978
- Current workaround: None. Admins cannot correctly view other users' sharing history, making the admin management functionality incomplete.

## Related API

- Endpoint: VFolder shared folder list API
- Field: inviter information
- Related PR: https://github.com/lablup/backend.ai-webui/pull/7609

JIRA Issue: BA-6231