feat(plugins): Add toggle support with lazy daemon instantiation (#1407)

Add togglePlugin() function and IPC command to toggle plugin visibility,
particularly for slideout-capable daemon plugins like AI Assistant.

Implementation uses lazy instantiation for daemon plugins:
- Daemons remain uninstantiated on load (respecting lifecycle)
- First toggle() call instantiates the daemon on-demand
- Subsequent toggles use the existing instance
- Prevents duplicate instantiation while supporting toggle functionality

This approach preserves the fix from f9b9d986 (ensure daemon plugins
not instantiated twice) while enabling new toggle capabilities.

Changes:
- Add PluginService.togglePlugin() with lazy instantiation
- Add DMSShellIPC plugin.toggle() command
- Maintains compatibility with existing daemon plugins

quickshell/DMSShellIPC.qml

@@ -966,6 +966,17 @@ Item {
             return success ? `PLUGIN_DISABLE_SUCCESS: ${pluginId}` : `PLUGIN_DISABLE_FAILED: ${pluginId}`;
         }
 
+        function toggle(pluginId: string): string {
+            if (!pluginId)
+                return "ERROR: No plugin ID specified";
+
+            if (!PluginService.availablePlugins[pluginId])
+                return `PLUGIN_NOT_FOUND: ${pluginId}`;
+
+            const success = PluginService.togglePlugin(pluginId);
+            return success ? `PLUGIN_TOGGLE_SUCCESS: ${pluginId}` : `PLUGIN_TOGGLE_FAILED: ${pluginId}`;
+        }
+
         function list(): string {
             const plugins = PluginService.getAvailablePlugins();
             if (plugins.length === 0)