feat(meals): customizable meal type visibility in Settings (#14)

Users can now toggle which meal types (breakfast, lunch, dinner, snack)
are displayed in the meal planner via a new Settings section. Preference
is stored household-wide in sync_config and applied as a filter on the
meals page. Includes preferences API, i18n (DE/EN/IT), and Settings UI.

public/locales/de.json

@@ -513,7 +513,12 @@
     "appleDisconnectConfirm": "Apple Calendar-Verbindung trennen?",
     "localeSystem": "System",
     "localeLabel": "Sprache",
-    "languageTitle": "Sprache"
+    "languageTitle": "Sprache",
+    "sectionMeals": "Essensplan",
+    "mealTypesLabel": "Sichtbare Mahlzeiten",
+    "mealTypesHint": "Nur ausgewaehlte Mahlzeit-Typen werden im Essensplan angezeigt.",
+    "mealTypesSaved": "Essensplan-Einstellungen gespeichert.",
+    "mealTypesMinOne": "Mindestens ein Mahlzeit-Typ muss aktiv sein."
   },
 
   "login": {