Add Home Manager service integration

README.md

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+# music-light
+
+`luz-musica.py` changes a Home Assistant light to match the active media artwork.
+
+## Home Manager integration
+
+This repository includes a Home Manager module at [home-manager/music-light.nix](/home/ltadeu6/music-light/home-manager/music-light.nix) that creates:
+
+- a `systemd --user` service called `music-light.service`
+- helper commands:
+  - `toggle-music-light`
+  - `start-music-light`
+  - `stop-music-light`
+  - `music-light-status`
+- an optional desktop launcher: `Music Light Toggle`
+
+### 1. Import the module
+
+Add this to your Home Manager configuration:
+
+```nix
+{
+  imports = [
+    /home/ltadeu6/music-light/home-manager/music-light.nix
+  ];
+
+  programs.music-light = {
+    enable = true;
+    scriptDir = "/home/ltadeu6/music-light";
+    pythonPath = "/usr/bin/python3";
+    playerctlPath = "/usr/bin/playerctl";
+    enableDesktopEntry = true;
+    autostart = false;
+  };
+}
+```
+
+If your Home Manager config is inside a flake, add the module to the relevant `homeManagerConfiguration`.
+
+### 2. Install the host runtime on Ubuntu
+
+On the Ubuntu host, install the runtime used by the service:
+
+```bash
+sudo apt update
+sudo apt install -y python3 python3-venv playerctl
+cd /home/ltadeu6/music-light
+python3 -m venv .venv
+. .venv/bin/activate
+pip install -r requirements.txt
+```
+
+Then point Home Manager at the venv interpreter:
+
+```nix
+programs.music-light.pythonPath = "/home/ltadeu6/music-light/.venv/bin/python";
+```
+
+If you prefer system-wide Python packages instead of a venv, keep `pythonPath = "/usr/bin/python3"` and make sure `requests` and `Pillow` are installed on the host.
+
+### 3. Apply Home Manager for the host user
+
+The service must run in the host user's `systemd --user`, not inside the Docker container.
+
+The Docker container can generate the Home Manager files as long as it writes into the real home directory used by the Ubuntu user. After activation, reload the user units on the host:
+
+```bash
+systemctl --user daemon-reload
+```
+
+Then control it with:
+
+```bash
+toggle-music-light
+music-light-status
+start-music-light
+stop-music-light
+journalctl --user -u music-light.service -f
+```
+
+### 4. Desktop button
+
+With `enableDesktopEntry = true`, Home Manager creates a launcher named `Music Light Toggle`.
+
+It typically appears in:
+
+- the application menu
+- launchers that read `.desktop` files
+- `~/.local/share/applications/`
+
+The generated launcher simply runs `toggle-music-light`, which starts or stops `music-light.service`.
+
+## Important detail about Docker + Ubuntu host
+
+If Home Manager is executed inside a container, that is fine for generating the user configuration files, but:
+
+- the target home directory must be the real home directory used by the host user
+- the service is started by the host's `systemd --user`
+- `python3`, `playerctl`, the virtualenv, and the media-session DBus must all be available on the host
+- the service must not point to executables that exist only inside the container or its `/nix/store`
+
+If `systemctl --user` inside the container does not control the host user session, run the final activation from the host side.