Refactor language-server command to use ThemeCommand's run method

Previously `theme language-server` command implemented
its own `run` logic. This commit refactors `language-server`
to use ThemeCommand's base `run()` method. This will help
to standardize command architecture and allow for
out of the box authentication and environments support

Author: dejmedus

packages/theme/src/cli/commands/theme/language-server.ts

@@ -13,8 +13,7 @@ export default class LanguageServer extends ThemeCommand {
     ...globalFlags,
   }
 
-  async run(): Promise<void> {
-    await this.parse(LanguageServer)
+  async command() {
     startServer()
   }
 }