Background threads (graph building, simulation prep, report generation,
profile generation) now inherit the requesting user's locale preference.
Previously these fell back to 'zh' because Flask request context was
unavailable in spawned threads.
- Remove traceback.format_exc() from all jsonify error responses
- Log tracebacks server-side with logger.exception() instead
- Prevents leaking internal stack traces to API consumers
- Updated README.md to reflect the removal of the project creation endpoint, adjusting the workflow steps accordingly.
- Removed the `create_project` function from graph.py, streamlining the project management API by eliminating deprecated functionality.