* fix: log progress tracker refresh errors instead of silently swallowing
The bare 'except Exception: pass' in StepTracker._maybe_refresh()
completely hid rendering bugs in the Rich progress display. Now logs
at DEBUG level with full traceback for diagnostics.
* test: add regression test for StepTracker refresh error logging
- Test that _maybe_refresh logs exceptions instead of silently swallowing
- Verify diagnostic message and traceback are recorded in DEBUG logs
- Confirm tracker update completes normally despite refresh callback failure
Requested by Copilot in PR #3975