Fix error handling, resource leaks, and logic bugs across the SDK

Bugs fixed:
- files.py: use typed error checking (_raise_for_status) instead of raw
  raise_for_status(), ensuring WrennNotFoundError etc. are raised
  correctly
- exceptions.py: check both "capsule_ids" and "sandbox_ids" response
  keys
  for backwards compatibility
- code_interpreter: retry _ensure_kernel on 5xx errors (only fail on
  4xx),
  remove redundant TimeoutError in bare except, clean up non-standard
  top-level msg_id/msg_type from Jupyter messages

Resource leaks fixed:
- capsule.py: close WrennClient if capsule creation or init fails
- code_interpreter: add close()/__del__ for _proxy_client cleanup when
  not using context manager

Logic fixes:
- pty.py: yield exit events to callers instead of silently discarding
  them
- capsule.py: auto-resume paused capsules in wait_ready instead of
  failing
- capsule.py: log warnings on destroy failure in __exit__ instead of
  silently swallowing errors

tests/test_client.py

@@ -23,13 +23,13 @@ BASE = "https://app.wrenn.dev/api"
 
 @pytest.fixture
 def client():
-    with WrennClient(api_key="wrn_test1234567890abcdef12345678") as c:
+    with WrennClient(api_key="wrn_test1234567890abcdef12345678", base_url=BASE) as c:
         yield c
 
 
 @pytest.fixture
 def async_client():
-    return AsyncWrennClient(api_key="wrn_test1234567890abcdef12345678")
+    return AsyncWrennClient(api_key="wrn_test1234567890abcdef12345678", base_url=BASE)
 
 
 class TestCapsules:
@@ -221,7 +221,8 @@ class TestAuthModes:
         with WrennClient(api_key="wrn_test1234567890abcdef12345678") as c:
             assert c._http.headers["X-API-Key"] == "wrn_test1234567890abcdef12345678"
 
-    def test_no_auth_raises(self):
+    def test_no_auth_raises(self, monkeypatch):
+        monkeypatch.delenv("WRENN_API_KEY", raising=False)
         with pytest.raises(ValueError, match="No API key"):
             WrennClient()