🚨 Issue Description

I'm using Backrest 1.13.0 on Armbian (ARM64) and Windows10 x64 system , trying to connect to Tencent Cloud COS (ap-guangzhou region) as the backup repository, but I keep getting the error:

`Stat: The bucket you are attempting to access must be addressed using COS virtual-styled domain.

The confusing part is that the exact same Restic command works perfectly when run directly in the terminal, but fails when executed through Backrest's UI.

📋 Environment Details

• Backrest version: 1.13.0
• OS/Arch: Armbian (Linux arm64) and Windows10 x64
• Restic version: 0.18.1
• Repository type: Tencent Cloud COS (ap-guangzhou region)
• Repository URI: `s3:https://cos.ap-guangzhou.myqcloud.com/linfuluantest-1300915121/PC2/

✅ Working Scenario (Terminal)

When I run this command directly in the shell, it connects successfully to the COS repository:
bash
export AWS_ACCESS_KEY_ID="ACCESS_KEY_ID"
export AWS_SECRET_ACCESS_KEY="SECRET_ACCESS_KEY"
restic init -r s3:https://cos.ap-guangzhou.myqcloud.com/linfuluantest-1300915121/PC2/ -o s3.bucket-lookup=dns -o s3.region=ap-guangzhou

Output: The repository is opened normally, no errors.

❌ Failing Scenario (Backrest UI)
When I configure the same repository in Backrest with these settings:
Repository URI: s3:https://cos.ap-guangzhou.myqcloud.com/linfuluantest-1300915121/PC2/
Password: [my repo password]
Environment Variables:
AWS_ACCESS_KEY_ID=AWS_ACCESS_KEY_ID
AWS_SECRET_ACCESS_KEY=AWS_SECRET_ACCESS_KEY
RESTIC_OPTS=-o s3.bucket-lookup=dns -o s3.region=ap-guangzhou
Testing the connection fails with:
Stat() returned error: The bucket you are attempting to access must be addressed using COS virtual-styled domain
It seems the RESTIC_OPTS parameter s3.bucket-lookup=dns is not being applied correctly when Backrest executes the Restic command.