fix: migrate legacy state to the first Discord server

tests/test_uploads_repository.py

@@ -0,0 +1,23 @@
+import tempfile
+import unittest
+from pathlib import Path
+
+from zyrarbot.storage.uploads_repository import UploadsRepository
+
+
+class UploadsRepositoryTest(unittest.TestCase):
+    def test_legacy_root_files_are_assigned_to_first_guild(self):
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            (root / "legacy.mp3").write_bytes(b"audio")
+            repository = UploadsRepository(str(root))
+
+            repository.migrate_legacy(10)
+
+            self.assertEqual([item.filename for item in repository.list(10)], ["legacy.mp3"])
+            self.assertFalse((root / "legacy.mp3").exists())
+            self.assertEqual(repository.list(20), [])
+
+
+if __name__ == "__main__":
+    unittest.main()