feat(renderer): mount ModalLayer + first-launch welcome trigger

src/renderer/hooks/use-welcome-trigger.ts

@@ -0,0 +1,15 @@
+import { useEffect } from 'react';
+import { useAppStore } from '@/stores/app-store';
+import { useSettingsStore } from '@/stores/settings-store';
+
+/**
+ * On first mount, if the user hasn't dismissed the welcome dialog, open it.
+ * Call once at the top of App.tsx.
+ */
+export function useWelcomeTrigger() {
+  useEffect(() => {
+    if (!useSettingsStore.getState().welcomeDismissed) {
+      useAppStore.getState().openModal('welcome');
+    }
+  }, []);
+}