fix: read public growth feature flag through SvelteKit

src/lib/growth-feature.ts

@@ -1 +1,3 @@
-export const growthFeatureEnabled = import.meta.env.PUBLIC_AI_GROWTH_ENABLED === 'true';
+import { PUBLIC_AI_GROWTH_ENABLED } from '$env/static/public';
+
+export const growthFeatureEnabled = PUBLIC_AI_GROWTH_ENABLED === 'true';