fix(windows-client): add proper error handling and pause before exit

Problem: Windows CLI client window closing immediately on error without error messages

Changes:
1. Wrapped main in error handler with pause before exit
2. Replaced .unwrap() with proper .context() error handling
3. Added pause on all error paths
4. Error display with colored output before exit
5. Updated ostp-client.exe checksum

Now on error:
- Error message displayed in red
- Press Enter to exit keeps window open
- User can read full error details

Note: NO GUI - ostp-client.exe is CLI tool
Usage:
- ostp-client.exe connect --server IP:PORT --psk KEY --country US
- ostp-client.exe setup (interactive wizard)

SHA256: 5612ae4503467d6d7b51c067f533706bc65b7b7ac41fccc3efaf3eda2576b92a

dist/windows-x64/SHA256SUMS.txt

@@ -1,3 +1,3 @@
-94400a0ab3a50a57d3914a905d79e1794a6e9642e63278854a9d492dd4f722ee  ostp-client.exe
+5612ae4503467d6d7b51c067f533706bc65b7b7ac41fccc3efaf3eda2576b92a  ostp-client.exe
 2e5c4dda1b0e9d1807892a3de587e4875906bdbe5343d5b83b5f33488d6e6696  ostp-daemon.exe
 8d0c759d4466e8b189ef161d6e0caac823e690bf5a82ee48308975d163728d7f  ostp-installer.exe