Beautify notification layout

[Pigbibi]

Summary

• split heartbeat holdings into sectioned list lines
• add localized execution detail heading and list formatting for logs
• cover translated headings and heartbeat layout in tests

Tests

• git diff --check
• .venv/bin/python -m pytest tests/test_rebalance_service.py tests/test_notifications.py -q
• .venv/bin/python -m pytest -q