test(04-01): add comprehensive tests for UserContextManager

- Add TestUserContext: tests for UserContext dataclass (creation, to_dict, from_dict)
- Add TestUserContextManager: tests for manager initialization and load
- Add TestAtomicWrites: tests for atomic save with backup rotation
- Add TestMultiUser: tests for multi-user isolation and convenience methods
- Add tmp_users_root and user_context_manager fixtures to conftest.py
- Export UserContext and UserContextManager from __init__.py

Note: Implementation was already done in commit 9bd29a2 as part of 04-02 plan.
This commit adds the tests that should have been part of 04-01 TDD workflow.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gsd-openclaw/tests/conftest.py

@@ -90,3 +90,32 @@ def sample_state() -> SessionState:
         last_output_snapshot="Test output snapshot",
         display_name="Test Project Display Name"
     )
+
+
+@pytest.fixture
+def tmp_users_root(tmp_path: Path) -> Path:
+    """Temporary root for user context testing.
+
+    This ensures tests don't pollute the real ~/gsd-workspaces/.users directory.
+
+    Args:
+        tmp_path: Pytest's built-in temporary directory fixture.
+
+    Returns:
+        Path to a temporary .users directory.
+    """
+    return tmp_path / "gsd-workspaces" / ".users"
+
+
+@pytest.fixture
+def user_context_manager(tmp_users_root: Path) -> "UserContextManager":
+    """UserContextManager with temporary root for isolation.
+
+    Args:
+        tmp_users_root: Fixture providing temporary user context root.
+
+    Returns:
+        UserContextManager instance configured for testing.
+    """
+    from gsd_openclaw.user_context import UserContextManager
+    return UserContextManager("test-user", tmp_users_root)