Harden Linux server runtime and packaging

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.

.gitignore

@@ -42,6 +42,7 @@ __pycache__/
 .mypy_cache/
 .ruff_cache/
 .venv/
+.venv-ci/
 venv/
 env/
 
@@ -49,5 +50,6 @@ env/
 *.log
 *.tmp
 *.bak
+logs/
 .DS_Store
 Thumbs.db