Fix division by zero in Docker image upload progress callback

[Copilot]

Addresses review feedback on PR #732 regarding potential division by zero when uploading empty Docker images.

Changes

• Added guard condition in progressCallback to return early when total == 0
• Prevents panic from percentage calculation float64(current) / float64(total) * 100 and progress bar width computation

progressCallback := func(current, total int64) {
    // Guard against division by zero
    if total == 0 {
        return
    }
    
    percentage := float64(current) / float64(total) * 100
    // ... rest of progress display logic
}

The callback silently skips progress updates for zero-byte files rather than crashing.

---

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[Copilot]

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