Add admin port support with other major refactorations

docker/README.md

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+# OpenTTD JGRPP Docker Server
+
+This setup builds OpenTTD with the JGR Patch Pack (JGRPP) from source and runs it in a Docker container.
+
+## Getting Started
+
+1.  **Build and start the server:**
+    ```bash
+    docker-compose up -d --build
+    ```
+
+2.  **Accessing the console:**
+    ```bash
+    docker exec -it openttd-jgrpp openttd -D
+    ```
+    (Actually, the server runs in dedicated mode. You can view logs with:)
+    ```bash
+    docker-compose logs -f
+    ```
+
+3.  **Configuration:**
+    The configuration is stored in `config/openttd.cfg`. The default password is set to `asd`.
+
+4.  **Save Games:**
+    Save games are stored in `config/save/`.
+
+## JGRPP Source
+The source code is cloned from the `jgrpp` branch of `https://github.com/JGRennison/OpenTTD-patches`.
+To update the server to a newer JGRPP version:
+1.  Update the `OpenTTD-patches` directory:
+    ```bash
+    cd OpenTTD-patches && git pull && cd ..
+    ```
+2.  Rebuild the image:
+    ```bash
+    docker-compose up -d --build
+    ```