docs: remove duplicate SANDBOX_REMOTE_MODE config entry

[CjiW]

Summary

During a scheduled documentation accuracy check, I found that the README.md configuration table had a duplicate entry for SANDBOX_REMOTE_MODE.

Changes

• Removed the duplicate SANDBOX_REMOTE_MODE entry from the Infrastructure configuration table

Verification

Checked the following for consistency:

• ✅ Directory structure matches actual code
• ✅ Makefile commands match README description
• ✅ Command list matches command_builtin.go
• ✅ Configuration items match config/config.go

Before

| `SANDBOX_MODE` | ... |
| `SANDBOX_REMOTE_MODE` | ... |  <- first occurrence
| ... |
| `SANDBOX_PUBLIC_URL` | ... |
| `SANDBOX_REMOTE_MODE` | ... |  <- duplicate
| `OAUTH_ENABLE` | ... |

After

| `SANDBOX_MODE` | ... |
| `SANDBOX_REMOTE_MODE` | ... |  <- only one occurrence
| ... |
| `SANDBOX_PUBLIC_URL` | ... |
| `OAUTH_ENABLE` | ... |