Fix Windows progress bar flickering issue

Problem

On Windows platforms, the progress bar exhibits significant flickering during updates due to differences in how Windows console handles carriage return (\r) characters compared to Unix/Linux systems.

Root Cause

The issue is in the clearProgressBar function where multiple \r operations are used:

str := fmt.Sprintf("\r%s\r", strings.Repeat(" ", s.maxLineWidth))

Windows console doesn't handle multiple \r operations as reliably as Unix/Linux terminals, causing visual artifacts.

Solution

• Added platform-specific handling for Windows
• Use minimal \r operation on Windows instead of full-line overwrite
• Maintain backward compatibility for Unix/Linux systems

Changes

• Added runtime import for platform detection
• Modified clearProgressBar function to use Windows-specific handling
• Simplified cursor control on Windows to reduce flickering

Testing

• ✅ Tested on Windows PowerShell
• ✅ Tested on Windows Terminal
• ✅ Verified no regression on Unix/Linux systems

Related Issue

Closes #219