docs(emulatorjs): add README

modules/20-services-apps/emulatorjs/README.md

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+# EmulatorJS Module
+
+This module deploys [EmulatorJS](https://github.com/linuxserver/docker-emulatorjs), a self-hosted retro gaming emulation platform, as a Docker container in the homelab environment.
+
+## Overview
+
+The EmulatorJS module:
+
+- Deploys the `linuxserver/emulatorjs` Docker container
+- Persists configuration and game data to volumes on the host
+- Exposes multiple ports for frontend, configuration, and backend services
+- Provides service definition for integration with networking modules
+
+## Usage
+
+```hcl
+module "emulatorjs" {
+  source      = "./modules/20-services-apps/emulatorjs"
+  volume_path = "/path/to/volumes/emulatorjs"
+}
+```
+
+## Variables
+
+| Variable      | Description                                  | Type     | Default    |
+| ------------- | -------------------------------------------- | -------- | ---------- |
+| `image_tag`   | Tag of the EmulatorJS image to use           | `string` | `"latest"` |
+| `volume_path` | Host path for EmulatorJS data volumes        | `string` | -          |
+
+## Outputs
+
+| Output               | Description                                                |
+| -------------------- | ---------------------------------------------------------- |
+| `service_definition` | Service definition for integration with networking modules |
+
+## Service Definition
+
+This module outputs a service definition that is used by the networking modules to expose the service.
+
+```hcl
+{
+  name         = "emulatorjs"
+  primary_port = <frontend_port>
+  endpoint     = "http://emulatorjs:<frontend_port>"
+}
+```
+
+Note that unlike other services, EmulatorJS doesn't specify subdomains or a publish method in its service definition. This may require manual configuration in your networking setup.
+
+## Ports
+
+EmulatorJS exposes three ports, which are mapped to host ports defined in the `.env` file:
+
+1. Frontend (port 80) - The main web interface for accessing games
+2. Config (port 3000) - The configuration interface
+3. Backend (port 4001) - Backend services
+
+## Environment Variables
+
+This module requires the following environment variables to be set in a `.env` file:
+
+- `EMULATORJS_FRONTEND_PORT`: Host port for the main web interface
+- `EMULATORJS_CONFIG_PORT`: Host port for the configuration interface
+- `EMULATORJS_BACKEND_PORT`: Host port for backend services
+
+## Data Persistence
+
+EmulatorJS stores its data in two volumes:
+
+1. Configuration: `/config` in the container, mapped to `${volume_path}/config` on the host
+2. Game data: `/data` in the container, mapped to `${volume_path}/data` on the host
+
+## Example Integration in Main Configuration
+
+```hcl
+module "emulatorjs" {
+  source      = "./modules/20-services-apps/emulatorjs"
+  volume_path = module.system_globals.volume_host
+}
+
+# If you want to expose EmulatorJS via your networking modules,
+# you may need to manually configure the service definition:
+module "services" {
+  source = "./modules/services"
+  # ...
+  service_definitions = [
+    module.emulatorjs.service_definition,
+    # Other service definitions
+  ]
+}
+```
+
+## Additional Configuration
+
+After deployment, you can access the configuration interface at `http://your-server:<config_port>` to:
+
+1. Upload ROM files to the `/data/roms` directory
+2. Configure emulation settings
+3. Manage game art and metadata