Adds end-to-end Linux compatibility work for the dedicated server: new CI workflow (Ubuntu + Arch), line-ending/executable safeguards, and a local venv-first startup flow with split dependency files for server vs optional host GUI tooling. Improves runtime resilience with better bind error messages, stricter config validation, writable-state checks, cleaner socket/thread shutdown behavior, and SIGTERM-aware graceful stop handling for headless/systemd use. Updates deployment/startup docs and adds portability/runtime integration tests to lock in these behaviors.
