fix: always get the latest migration even when two are applied at the same time

without also ordering by migration_name, two migrations being applied at
the same time *can* (but won't always) result in the *earlier* migration
being returned as the latest one. as our migrations are not idempotent,
this causes the bot to crash on startup (and even if they *were*
idempotent, the code that inserts the new migration name into the
migrations table isn't)

Catalogger.Backend/Database/DatabaseMigrator.cs

@@ -141,7 +141,7 @@ public class DatabaseMigrator(ILogger logger, IClock clock, DatabaseConnection c
         if (hasMigrationTable)
         {
             return await conn.QuerySingleOrDefaultAsync<MigrationEntry>(
-                "SELECT * FROM migrations ORDER BY applied_at DESC LIMIT 1"
+                "SELECT * FROM migrations ORDER BY applied_at DESC, migration_name DESC LIMIT 1"
             );
         }
 
@@ -163,7 +163,7 @@ public class DatabaseMigrator(ILogger logger, IClock clock, DatabaseConnection c
         return await reader.ReadToEndAsync();
     }
 
-    public static IEnumerable<string> GetMigrationNames() =>
+    private static IEnumerable<string> GetMigrationNames() =>
         typeof(DatabasePool)
             .Assembly.GetManifestResourceNames()
             .Where(s => s.StartsWith($"{RootPath}.Migrations"))