Add integration tests against a local Temporal server

Current tests are unit-level with mocks, so they can't catch runtime issues like event-loop blocking on auth I/O (see #33). We should have a lightweight integration suite that spins up a local Temporal dev server and runs a basic connect + workflow against it.

Scope is open, even one smoke test (connect, run a trivial workflow, assert it completes) would close most of the gap.
Doesn't need to be exhaustive.

Start by reviewing the current unit tests and the runtime concern described in #33, then determine how this Python library can launch a local Temporal dev server. Add a lightweight integration smoke test that connects, runs a trivial workflow, and asserts completion. Done means the test runs against the local server without mocks and passes reliably.

Written by the indexing model from the issue text.