add: harden thumbnail generation and validate image assets

scripts/lib/meals.js

@@ -47,6 +47,8 @@ function validateMeals(meals) {
     throw new Error("data/meals.json must contain an array");
   }
 
+  const ids = new Set();
+
   for (const [index, meal] of meals.entries()) {
     if (!meal || typeof meal !== "object") {
       throw new Error(`Meal at index ${index} must be an object`);
@@ -62,6 +64,12 @@ function validateMeals(meals) {
       throw new Error(`Meal ${index} has a non-string "position" value`);
     }
 
+    if (ids.has(meal.id)) {
+      throw new Error(`Duplicate meal id "${meal.id}" found in data/meals.json`);
+    }
+
+    ids.add(meal.id);
+
     validateThumbnail(meal, index);
   }
 }