fix(analyze): drop unused drift import in shuffle_source

Query-builder methods come through the generated AppDb, not the
drift package directly — the import was dead. (#427 S4a)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/lib/cache/shuffle_source.dart

@@ -10,7 +10,6 @@
 
 import 'dart:math';
 
-import 'package:drift/drift.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../library/library_providers.dart' show libraryApiProvider;