Adds a production-safe headphone-splitter mode:
- Device bytes tee'd to both --upstream (primary/prod) and --mirror (new server)
- Only primary server responses are returned to the device
- Mirror connect/write failures are non-fatal and logged; prod is unaffected
- New raw_mirror_<ts>.bin capture file alongside raw_client/raw_server
Three modes: standalone (capture only), bridge (one upstream), splitter (two).
Default listen port changed to 12345 to match project ACH setup.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>