feat(multi-vertical): phase 0 — seed data script + fix GetShopsQueryHandler NullRef

- Add scripts/seed-demo-data.sh: creates user, merchant, 5 shops, 47 products, 15 categories, 18 tables/rooms, 13 booking resources
- Fix NullReferenceException in GetShopsQueryHandler (null-safe Enumeration access)
- Default account: hongochai10@icloud.com / Velik@2026

services/merchant-service-net/src/MerchantService.API/Application/Queries/Shops/GetShopsQueryHandler.cs

@@ -51,11 +51,11 @@ public class GetMyShopsQueryHandler : IRequestHandler<GetMyShopsQuery, IReadOnly
             Id = s.Id,
             Name = s.Name,
             Slug = s.Slug,
-            Type = s.Type.Name,
-            Category = s.Category.Name,
-            Status = s.Status.Name,
+            Type = s.Type?.Name ?? "Unknown",
+            Category = s.Category?.Name ?? "Other",
+            Status = s.Status?.Name ?? "Unknown",
             LogoUrl = s.LogoUrl,
-            BranchCount = s.Branches.Count,
+            BranchCount = s.Branches?.Count ?? 0,
             CreatedAt = s.CreatedAt
         }).ToList();
     }