test(ui): make provider auto-sync fixtures deterministic

[diegosouzapw]

Summary

• Use the shared stable translation fixture instead of recreating the translation function on every render.
• Replace the 10ms wall-clock sleep with act-driven, controlled timers and explicit unmount cleanup.
• Add a populated-catalog regression that proves loading does not restart on unrelated state updates.

Evidence

• The original suite passed 5/5 locally, while integrated CI reported the asynchronous sync failure; this is not claimed as a deterministic original BASE-RED.
• Restoring the old unstable translation mock against the new focused regression reproduced a timeout and teardown failures.
• The corrected suite passed 6/6 in two consecutive runs; assertions and timeouts were not relaxed.
• Production hook and authentication behavior are unchanged.

Part of quality-gate recovery. Draft pending integrated CI and owner review.