Split the monolithic test server into a reusable server core and a thin terminal launcher, and add a PySide6 developer GUI. Added server_core.py (FalloutTogetherServer) with lifecycle control, thread-safe client snapshots, stats and log listener support; added client_session.py for per-client state; added dev_server_app.py GUI and requirements.txt. Updated server.py to use the new server core, and revised server/README.md and docs/dev-log.md to document the new structure, usage, and validation steps. Protocol behavior (welcome/transform/disconnect handling and newline-separated JSON) remains unchanged.
