fix(schema): handle backwards compat for dir.app

Author: danielroe

packages/schema/src/config/common.ts

@@ -301,7 +301,8 @@ export default defineUntypedSchema({
       $resolve: async (val: string | undefined, get) => {
         const isV4 = (await get('future') as Record<string, unknown>).compatibilityVersion === 4
         if (isV4) {
-          return resolve(await get('srcDir') as string, val || '.')
+          const [srcDir, rootDir] = await Promise.all([get('srcDir') as Promise<string>, get('rootDir') as Promise<string>])
+          return resolve(await get('srcDir') as string, val || (srcDir === rootDir ? 'app' : '.'))
         }
         return val || 'app'
       },