feat(docker): add Dockerfile, docker-compose and headless fallback for local testing

tests/test_config.py

@@ -36,3 +36,17 @@ kodi_rpc:
         assert cfg.kodi_rpc.http_port == 8088
     finally:
         Path(f_path).unlink()
+
+
+def test_env_var_overrides(monkeypatch):
+    monkeypatch.setenv("JELLYFIN_SERVER_URL", "https://override.lan")
+    monkeypatch.setenv("JELLYFIN_USERNAME", "envuser")
+    monkeypatch.setenv("MPV_VO", "null")
+    monkeypatch.setenv("MPV_FULLSCREEN", "true")
+
+    cfg = AppConfig.load()
+    assert cfg.jellyfin.server_url == "https://override.lan"
+    assert cfg.jellyfin.username == "envuser"
+    assert cfg.player.vo == "null"
+    assert cfg.player.fullscreen is True
+