feat: build themes into a centralised plugin

src/plugins/built-in/themes/index.ts

@@ -0,0 +1,54 @@
+import type { Plugin } from '../../core/types';
+import { BasePlugin, BooleanSetting } from '../../core/settings';
+import { ThemeManager } from './theme-manager';
+
+// Define only the typed settings - no need for redundant interface
+class ThemePluginClass extends BasePlugin {
+  @BooleanSetting({
+    default: true,
+    title: "Themes",
+    description: "Adds a theme selector to the settings page"
+  })
+  enabled!: boolean;
+}
+
+// Create an instance to extract settings
+const settingsInstance = new ThemePluginClass();
+
+const themesPlugin: Plugin<typeof settingsInstance.settings> = {
+  id: 'themes',
+  name: 'Themes',
+  description: 'Adds a theme selector to the settings page',
+  version: '1.0.0',
+  settings: settingsInstance.settings,
+  run: async (api) => {
+    console.debug('[ThemesPlugin] Starting plugin');
+    const themeManager = ThemeManager.getInstance();
+
+    if (api.settings.enabled) {
+      console.debug('[ThemesPlugin] Plugin enabled, initializing theme manager');
+      await themeManager.initialize();
+    }
+    
+    const enabledCallback = (value: string | number | boolean) => {
+      console.debug('[ThemesPlugin] Enabled setting changed:', value);
+      if (value === true) {
+        console.debug('[ThemesPlugin] Plugin enabled, initializing theme manager');
+        void themeManager.initialize();
+      } else if (value === false) {
+        console.debug('[ThemesPlugin] Plugin disabled, cleaning up theme manager');
+        void themeManager.cleanup();
+      }
+    }
+    
+    api.settings.onChange('enabled', enabledCallback);
+    
+    return () => {
+      console.debug('[ThemesPlugin] Plugin cleanup');
+      api.settings.offChange('enabled', enabledCallback);
+      void themeManager.cleanup();
+    }
+  }
+};
+
+export default themesPlugin;