docs: update docker config and docs for white labeling

WHITE_LABEL.md

@@ -65,3 +65,35 @@ To replace the logo and icons:
 1.  Replace `public/favicon.ico`.
 2.  Replace `public/icon.png` (if it exists).
 3.  Update `app/manifest.ts` if you have custom icon paths.
+3.  Update `app/manifest.ts` if you have custom icon paths.
+
+## Docker Deployment
+
+When deploying with Docker, please note that **Next.js inlines `NEXT_PUBLIC_` environment variables at build time**.
+
+This means you cannot simply change the environment variables in `docker-compose.yml` and restart the container to change the branding. You must **rebuild the image**.
+
+### Using Docker Compose
+
+1.  Create a `.env` file with your custom configuration:
+    ```bash
+    NEXT_PUBLIC_APP_NAME="My Music Game"
+    NEXT_PUBLIC_THEME_COLOR="#ff0000"
+    # ... other variables
+    ```
+
+2.  Ensure your `docker-compose.yml` passes these variables as build arguments (already configured in `docker-compose.example.yml`):
+    ```yaml
+    services:
+      hoerdle:
+        build:
+          context: .
+          args:
+            NEXT_PUBLIC_APP_NAME: ${NEXT_PUBLIC_APP_NAME}
+            # ...
+    ```
+
+3.  Build and start the container:
+    ```bash
+    docker compose up --build -d
+    ```