style(harness): move test_session_mutations imports to top, drop unused json

harness/tests/test_session_mutations.py

@@ -1,6 +1,8 @@
 """Tests for session manifest mutations (rename, group, archive, delete)."""
 import pytest
+from typer.testing import CliRunner
 
+from tht.cli.session_cmd import session_app
 from tht.config import DatabaseConfig
 from tht.session.store import (
     SessionError,
@@ -69,12 +71,6 @@ def test_delete_missing_raises(tmp_path):
         delete_session("nope", tmp_path)
 
 
-import json
-from typer.testing import CliRunner
-
-from tht.cli.session_cmd import session_app
-
-
 def _patch_cfg(monkeypatch, tmp_path):
     from tht.cli import session_cmd