feat(ausstellungen): Ausstellungs-/Auszeichnungsergebnisse je Tier

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

GerbilManagerWebAPI/ApplicationContext.cs

@@ -25,6 +25,7 @@ public class ApplicationContext : DbContext
     public DbSet<Request> Requests => Set<Request>();
     public DbSet<MailSettings> MailSettings => Set<MailSettings>();
     public DbSet<Feedback> Feedback => Set<Feedback>();
+    public DbSet<ExhibitionResult> ExhibitionResults => Set<ExhibitionResult>();
 
     // Keep Gerbil.NameSearch in sync on every save (separator-insensitive search key),
     // so it can never drift from Name regardless of which code path mutates the entity.
@@ -212,6 +213,14 @@ public class ApplicationContext : DbContext
             e.HasIndex(f => f.CreatedAt);
         });
 
+        // EXHIBITION: deliberately relationship-free (same pattern as Feedback). GerbilId is a
+        // plain nullable Guid column (no navigation property → EF creates NO foreign key), so the
+        // import re-ingest wipe of Gerbils never cascades into or breaks exhibition rows.
+        modelBuilder.Entity<ExhibitionResult>(e =>
+        {
+            e.HasIndex(x => x.GerbilId);
+        });
+
         // DB-4: German collation on remaining searched/sorted text columns (Npgsql-only).
         if (isNpgsql)
         {