Add admin port support with other major refactorations

docker/docker-compose.yml

@@ -0,0 +1,25 @@
+services:
+  openttd:
+    build: .
+    container_name: openttd-jgrpp
+    restart: unless-stopped
+    ports:
+      - "3979:3979/tcp"
+      - "3979:3979/udp"
+      - "3977:3977/tcp"
+    volumes:
+      - ./config:/home/openttd/.local/share/openttd
+    environment:
+      - PUID=1000
+      - PGID=1000
+    # Use exec to ensure openttd receives SIGTERM directly for autosave_on_exit
+    command: >
+      bash -c "
+      if [ -f /home/openttd/.local/share/openttd/save/autosave/exit.sav ]; then
+        echo 'Found autosave/exit.sav, loading...'
+        exec openttd -D -g save/autosave/exit.sav
+      else
+        exec openttd -D
+      fi"
+    stop_signal: SIGTERM
+    stop_grace_period: 30s