fix: What's New overlay reappearing despite dismissal

The appVersion was read via a fragile cast chain that could resolve
to '0.0.0' at runtime, so acknowledgeNewVersion() saved the wrong
version string and the overlay reappeared on every page load.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: InfantLab

app/composables/useOnboarding.ts

@@ -71,7 +71,7 @@ function saveState() {
 
 export function useOnboarding() {
   const config = useRuntimeConfig();
-  const currentVersion = ((config as unknown as Record<string, Record<string, unknown>>)['public']!)['appVersion'] as string || "0.0.0";
+  const currentVersion = String(config.public?.appVersion ?? "0.0.0");
 
   // Initialize on mount — safe to call multiple times since all
   // instances share the same state ref