fix(state): surface localStorage save failures instead of silent loss (#4)

saveState now logs a console.warn on failure and alerts the user once per
session (storage full/unavailable) so they can export their data and avoid
silent data loss.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

js/app.js

@@ -31,6 +31,7 @@ try {
 }
 
 // Call after any state mutation to persist automatically
+let storageWarned = false;
 export function saveState() {
   try {
     localStorage.setItem(STORAGE_KEY, JSON.stringify({
@@ -39,8 +40,15 @@ export function saveState() {
       history: state.history,
       settings: state.settings
     }));
-  } catch {
+  } catch (e) {
-    // Storage full or unavailable — silently ignore
+    // Storage full or unavailable — warn once so the user can react (export data)
+    console.warn('Speichern in localStorage fehlgeschlagen:', e);
+    if (!storageWarned) {
+      storageWarned = true;
+      alert('Achtung: Änderungen konnten nicht gespeichert werden ' +
+        '(Speicher voll oder nicht verfügbar). Bitte exportiere deine Daten ' +
+        'als JSON, um Datenverlust zu vermeiden.');
+    }
   }
 }