fix: address PR #5 review comments

- Add class-level type annotations on TrelloClient (api_key, token, _session)
- Add TypedDict response contracts with TypeGuard narrowing for _request
- Replace os.environ manipulation with monkeypatch in tests
- Align disconnect message with auto-reconnect behavior
- Add docstring for TRELLO_API_BASE constant
- Add _post and _put request helpers for future endpoints

tests/test_auth.py

@@ -8,6 +8,7 @@ from collections.abc import Generator
 from typing import Any
 
 import pytest
+from pytest import MonkeyPatch
 import requests
 
 # Tell pytest we plan to set env vars in tests
@@ -19,16 +20,11 @@ pytestmark = pytest.mark.usefixtures("clear_env")
 # ---------------------------------------------------------------------------
 
 @pytest.fixture(autouse=True)
-def clear_env() -> Generator[None, None, None]:
+def clear_env(monkeypatch: MonkeyPatch) -> Generator[None, None, None]:
     """Remove Trello env vars before each test so state is predictable."""
-    # Use monkeypatch via request directly — fallback to os.environ
-    saved_key = os.environ.pop("TRELLO_API_KEY", None)
-    saved_token = os.environ.pop("TRELLO_TOKEN", None)
+    monkeypatch.delenv("TRELLO_API_KEY", raising=False)
+    monkeypatch.delenv("TRELLO_TOKEN", raising=False)
     yield
-    if saved_key is not None:
-        os.environ["TRELLO_API_KEY"] = saved_key
-    if saved_token is not None:
-        os.environ["TRELLO_TOKEN"] = saved_token
 
 
 def _make_session(mocker: Any) -> requests.Session: