skill(dms-plugin-dev): update for composite plugins, startupCheck, IPC discovery (#2699)

- Add composite plugin type with multi-surface components field
- Add startupCheck manifest field and dependency gating docs
- Add IPC runtime plugin discovery commands (plugin-scan target)
- Add getPluginPath() to data persistence reference
- Document bar reveal visibility optimization for widget plugins
- Sync plugin-schema.json with source, add dependencies field
- Bump skill version to 1.1

.agents/skills/dms-plugin-dev/references/data-persistence-guide.md

@@ -166,6 +166,16 @@ function increment() {
 | Cross-instance sync (multi-monitor data) | `PluginGlobalVar` or `getGlobalVar`/`setGlobalVar` | No (runtime only) | All instances |
 | Quick reactive reads from settings | `pluginData` property | N/A (read-only) | Per instance |
 
+## Plugin Path
+
+Retrieve a plugin's installation directory at runtime:
+
+```qml
+var dir = pluginService.getPluginPath(pluginId)
+```
+
+Returns the absolute path to the plugin's directory (e.g., `~/.config/DankMaterialShell/plugins/MyPlugin`), or an empty string if the plugin is not found. Useful for loading bundled assets (images, data files) relative to the plugin's location.
+
 ## Important Notes
 
 1. **pluginData is reactive** - bindings update automatically when data changes