refactor: extract model flag and simplify config return type

src/config/index.ts

@@ -8,16 +8,14 @@ export interface AppConfig {
   model?: string;
 }
 
-export async function loadConfig(): Promise<{
-  config: AppConfig;
-}> {
+export async function loadConfig(): Promise<AppConfig> {
   let config: AppConfig;
   try {
     config = await configFile.json();
   } catch {
     config = {};
   }
-  return { config };
+  return config;
 }
 
 export async function saveConfig(config: AppConfig): Promise<void> {