fix(email-data): replace hardcoded emailApi schema string with MigrationConstants

Down migration was referencing "emailApi" literal instead of MigrationConstants.SchemaName,
which would have dropped the wrong schema on rollback. Also fix stale comment in DbContext.

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

Apis/email-data/EmailApiDbContext.cs

@@ -15,7 +15,7 @@ public sealed class EmailApiDbContext : DbContext
     protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
     {
         base.OnConfiguring(optionsBuilder);
-        // Configure migration history table to use schema-qualified name: [emailApi].[_Migrations]
+        // Configure migration history table to use schema-qualified name: [email].[_Migrations]
         optionsBuilder.UseSqlServer(x => x.MigrationsHistoryTable(MigrationTableName, SchemaName));
     }
 

Apis/email-data/Migrations/20260528100000_CreateEmailTemplates.cs

@@ -185,7 +185,7 @@ namespace Email.Data.Migrations
         /// <inheritdoc />
         protected override void Down(MigrationBuilder migrationBuilder)
         {
-            migrationBuilder.DropTable(name: "EmailTemplates", schema: "emailApi");
+            migrationBuilder.DropTable(name: "EmailTemplates", schema: MigrationConstants.SchemaName);
         }
     }
 }