feat: add Wayland Screen Mirror plugin (#86)

* feat: add wl-screen-mirror plugin

* fix: naming

* rename thumbnail

* fix(error): treat user termination as a clean stop

wl-screen-mirror/README.md

@@ -0,0 +1,36 @@
+# Wayland Screen Mirror
+
+This plugin allows you to easily toggle screen mirroring in Wayland via `wl-mirror`.
+
+## Plugin
+
+| Field | Value |
+| --- | --- |
+| ID | `elijaharch/wl-screen-mirror` |
+| Entries | Bar widget: `mirror`; panel: `controls`; service: `mirror-service` |
+
+## Requirements
+
+- [`wl-mirror`](https://github.com/Ferdi265/wl-mirror) available on `PATH`
+
+## Usage
+
+1. Add the `mirror` widget to your bar
+2. Open the panel and select the source and destination displays
+3. Click on **Start mirroring**
+
+```sh
+noctalia msg panel-toggle elijaharch/wl-screen-mirror:controls
+```
+
+The service stops mirroring automatically if either selected output disconnects.
+
+## Notes
+
+- The plugin launches
+  `wl-mirror --fullscreen-output DESTINATION --fullscreen SOURCE`.
+- A private marker and the latest `wl-mirror` error output are written under the
+  plugin data directory. No user content is stored.
+- The managed process is terminated when mirroring stops, the plugin reloads,
+  or Noctalia exits. Other `wl-mirror` processes are not affected.
+- The plugin makes no network requests.