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/src/gsd_openclaw/__init__.py

@@ -14,6 +14,7 @@ from gsd_openclaw.command_executor import CommandResult, OutputCapture, CommandE
 from gsd_openclaw.approval_handler import ApprovalHandler, ApprovalState
 from gsd_openclaw.progress_monitor import ProgressMonitor, ProgressInfo
 from gsd_openclaw.orchestrator import Orchestrator
+from gsd_openclaw.user_context import UserContext, UserContextManager
 
 __all__ = [
     "SessionState",
@@ -33,4 +34,6 @@ __all__ = [
     "ProgressMonitor",
     "ProgressInfo",
     "Orchestrator",
+    "UserContext",
+    "UserContextManager",
 ]