feat(plans): menu watermark on Free (removed by paid feature)

Guest QR menu shows a "ساخته‌شده با میزی" watermark under the menu unless the café's
plan has the `watermark_removed` feature (Starter+).

- PublicMenuDto gains ShowWatermark; PublicService computes it from
  IsFeatureEnabledForCafeAsync("watermark_removed") for both slug and branch menus.
- Guest menu renders the watermark footer when showWatermark.
- NoOpPlatformCatalogService test double (all features on) for the PublicService
  ctor; QrMenuTests updated.

86 tests pass; dashboard tsc clean.

tests/Meezi.API.Tests/QrMenuTests.cs

@@ -120,7 +120,7 @@ public class QrMenuTests
         var http = new HttpContextAccessor();
         var media = new NoOpMediaStorageService();
         var reviews = new ReviewService(db, abuse, http, media);
-        var publicSvc = new PublicService(db, orders, reviews, kds, branchMenu, identity, abuse, http);
+        var publicSvc = new PublicService(db, orders, reviews, kds, branchMenu, identity, abuse, http, new NoOpPlatformCatalogService());
 
         return (db, tables, publicSvc, cafeId, branchId, tableId, itemA, itemB, qrCode);
     }