[CI] Fix: Windows-specific build failure

[CaseyLabs]

Summary

• fix the Windows release cross-build failure
• keep the change scoped to cross-platform signal handling and the copyover reconnect-token hook

Root Cause

• main.go referenced syscall.SIGTSTP unconditionally, which does not exist on Windows
• connections.IssueWebSocketReconnectToken was only declared in the Unix-specific file, so Windows builds could not compile main.go

Changes

• add OS-specific shutdown signal helpers for Unix and Windows
• keep SIGTSTP on Unix only
• declare the reconnect-token hook in the Windows connections file so the shared wiring in main.go compiles on both platforms

Validation

• GOOS=windows GOARCH=amd64 go build -v -o /tmp/go-mud-windows_x64.exe .
• go test ./internal/connections ./internal/copyover

Impact

• release workflows can now complete the Windows build step
• no intended behavior change for Unix runtime handling

[Volte6]

Good change. What do you think about consolidating these signals changes with those found in copyover_signal_unix.go and copyover_signal_windows.go?

Maybe signals_unix.go and signals_windows.go? That way we don't incrementally add more and more files everytime we have new signals we want to add.

[CaseyLabs]

@Volte6 - made the following change in commit 151bf94 ... is this what you had in mind? No worries if I misunderstood.

Consolidated the OS-specific signal handling into signals_unix.go and signals_windows.go, moving the shutdown and copyover signal helpers into those two platform files without changing behavior. This keeps the Windows fix intact while avoiding additional one-off signal files.