Keep miniupnpc as the active UPnP backend

Summary

The proposed switch from UPnPImplMiniLib (miniupnpc) to UPnPImplWinServ as the default backend is declined.

Current main keeps the existing UPnP implementation mix rather than forcing a backend change and removing miniupnpc from the workspace.

Why This Is Wont-Fix

• This is not just dependency cleanup; it changes live networking behavior.
• UPnP success is router- and stack-sensitive, so keeping the broader current compatibility surface is the lower-risk choice.
• The branch direction favors hardening and compatibility preservation over replacing active network plumbing for cleanup reasons.

Disposition

• Marked Wont-Fix
• Keep miniupnpc in the UPnP stack
• Revisit only if a concrete, reproducible bug or maintenance blocker makes the current arrangement unacceptable