feat: add MyWhoosh token persistence

tests/mywhoosh/test_tokenstore.py

@@ -0,0 +1,18 @@
+from pathlib import Path
+
+from app.mywhoosh.models import MyWhooshToken
+from app.mywhoosh.tokenstore import MyWhooshTokenStore
+
+
+def test_tokenstore_round_trip_and_permissions(tmp_path: Path) -> None:
+    store = MyWhooshTokenStore(tmp_path / "tokens" / "7" / "mywhoosh.json")
+    token = MyWhooshToken(access_token="access", refresh_token="refresh", whoosh_id="whoosh-7")
+    store.save(token)
+
+    assert store.load() == token
+    assert oct(store.path.stat().st_mode & 0o777) == "0o600"
+
+
+def test_missing_token_returns_none(tmp_path: Path) -> None:
+    store = MyWhooshTokenStore(tmp_path / "missing.json")
+    assert store.load() is None