fix(demo): scope category/item IDs per café to prevent PK collisions

DemoMenuSeeder used hardcoded IDs like cat_demo_coffee for every café.
If the dev seeder (runs when ASPNETCORE_ENVIRONMENT=Development) already
inserted those IDs for cafe_demo_001, a production café clicking
"Add demo data" hit a primary-key constraint violation.

Fix: EnsureMenuAsync now accepts useScopedIds=true which prefixes every
category and item ID with cafeId (e.g. cafe_abc_cat_demo_coffee).
CategoryId FKs on items are remapped through the same function.

DemoSeedService (the API endpoint handler) always passes useScopedIds=true.
DevelopmentDataSeeder keeps useScopedIds=false (default) so the existing
cafe_demo_001 rows in dev databases are not touched.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Meezi.API/Services/DemoSeedService.cs

@@ -56,10 +56,12 @@ public class DemoSeedService : IDemoSeedService
                 .FirstAsync(ct);
         }
 
-        // 2. Seed menu (categories + items) using café-agnostic seeder
+        // 2. Seed menu (categories + items) using café-agnostic seeder.
+        // useScopedIds=true prefixes all IDs with cafeId so multiple cafés
+        // can each have their own demo menu without primary-key collisions.
         var beforeCats = await _db.MenuCategories.CountAsync(c => c.CafeId == cafeId, ct);
         var beforeItems = await _db.MenuItems.CountAsync(i => i.CafeId == cafeId, ct);
-        await DemoMenuSeeder.EnsureMenuAsync(_db, cafeId, taxId, _logger);
+        await DemoMenuSeeder.EnsureMenuAsync(_db, cafeId, taxId, _logger, useScopedIds: true);
         var afterCats = await _db.MenuCategories.CountAsync(c => c.CafeId == cafeId, ct);
         var afterItems = await _db.MenuItems.CountAsync(i => i.CafeId == cafeId, ct);
 

src/Meezi.Infrastructure/Data/DemoMenuSeeder.cs

@@ -6,8 +6,23 @@ namespace Meezi.Infrastructure.Data;
 
 public static class DemoMenuSeeder
 {
-    public static async Task EnsureMenuAsync(AppDbContext db, string cafeId, string taxId, ILogger logger)
+    /// <param name="useScopedIds">
+    /// When true, category and item IDs are prefixed with <paramref name="cafeId"/> so
+    /// multiple cafés can each have their own copy of the demo menu without a primary-key
+    /// collision.  Pass false only for the legacy demo café (cafe_demo_001) whose IDs are
+    /// already in the database without a café prefix.
+    /// </param>
+    public static async Task EnsureMenuAsync(
+        AppDbContext db, string cafeId, string taxId, ILogger logger,
+        bool useScopedIds = false)
     {
+        // When useScopedIds=true every row gets a deterministic ID that is unique per café:
+        //   category  →  "{cafeId}_{catalogId}"
+        //   item      →  "{cafeId}_{catalogId}"
+        // The catalog item's CategoryId is remapped through the same function.
+        string Scoped(string catalogId) =>
+            useScopedIds ? $"{cafeId}_{catalogId}" : catalogId;
+
         if (!await db.Taxes.AnyAsync(t => t.Id == taxId && t.CafeId == cafeId))
         {
             db.Taxes.Add(new Tax
@@ -29,7 +44,8 @@ public static class DemoMenuSeeder
         var categoriesAdded = 0;
         foreach (var cat in DemoMenuCatalog.Categories)
         {
-            if (existingCategoryIds.TryGetValue(cat.Id, out var row))
+            var catId = Scoped(cat.Id);
+            if (existingCategoryIds.TryGetValue(catId, out var row))
             {
                 if (string.IsNullOrWhiteSpace(row.Icon) && !string.IsNullOrWhiteSpace(cat.Icon))
                     row.Icon = cat.Icon;
@@ -46,7 +62,7 @@ public static class DemoMenuSeeder
 
             db.MenuCategories.Add(new MenuCategory
             {
-                Id = cat.Id,
+                Id = catId,
                 CafeId = cafeId,
                 Name = cat.Name,
                 NameEn = cat.NameEn,
@@ -69,14 +85,15 @@ public static class DemoMenuSeeder
         var itemsAdded = 0;
         foreach (var item in DemoMenuCatalog.Items)
         {
-            if (existingItemIds.Contains(item.Id))
+            var itemId = Scoped(item.Id);
+            if (existingItemIds.Contains(itemId))
                 continue;
 
             db.MenuItems.Add(new MenuItem
             {
-                Id = item.Id,
+                Id = itemId,
                 CafeId = cafeId,
-                CategoryId = item.CategoryId,
+                CategoryId = Scoped(item.CategoryId),   // FK must point at scoped category ID
                 Name = item.Name,
                 NameEn = item.NameEn,
                 NameAr = item.NameAr,