refactor(config): move storybook and vitest configs to config/, import app.css in storybook preview

config/storybook/vitest.setup.ts

@@ -0,0 +1,7 @@
+import * as a11yAddonAnnotations from "@storybook/addon-a11y/preview";
+import { setProjectAnnotations } from '@storybook/sveltekit';
+import * as projectAnnotations from './preview';
+
+// This is an important step to apply the right configuration when testing your stories.
+// More info at: https://storybook.js.org/docs/api/portable-stories/portable-stories-vitest#setprojectannotations
+setProjectAnnotations([a11yAddonAnnotations, projectAnnotations]);