fix: prevent exception message exposure via unauthenticated /api/settings endpoint

[Copilot]

GET /api/settings requires no authentication and returns dataUpdateStatus, which included raw exception messages (str(e)) from failed data sync runs. This leaked internal details (file paths, API responses, etc.) to any external user.

Changes

• data_update.py — In run_data_update, log the full exception server-side first, then assign a generic string to error_message instead of str(e). This generic message is what propagates into the status dict, persisted to disk, and ultimately returned to clients.

# Before
error_message = str(e)
logger.error(f"Error updating employee data: {e}")

# After
logger.error(f"Error updating employee data: {e}")
error_message = 'Data update failed due to an internal error.'

Full exception detail is preserved in server logs; only the opaque message reaches the HTTP response.

[Copilot]

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