Fix SoundBridgeHost signal handler lifetime

[rustydomino]

• Fid DSP test runner path
• Fix host signal handler lifetime

Summary

Fixes SoundBridgeHost not responding to SIGINT or SIGTERM when run standalone.

Problem

The DispatchSourceSignal instances created in setupSignalHandlers() were local variables. After the function returned, they were released while SIGINT and SIGTERM remained configured with SIG_IGN.

As a result, Ctrl+C and normal SIGTERM termination had no effect on the running host.

Fix

Retain the signal dispatch sources for the lifetime of the host process.

Testing

Verified that:

• Ctrl+C now triggers the existing SIGINT handler and cleanup path.
• SIGTERM now triggers the existing SIGTERM handler and cleanup path.
• SoundBridgeHost exits after cleanup in both cases.