Fix react-compiler warnings: mutations, debounce, and delete patterns in admin UI

Summary

Fix react-compiler/react-compiler warnings in the admin UI that are not related to useRoutableTab hook wrappers:

• Rename useRefreshTokens watch value to avoid false-positive hook detection
• Replace useCallback(debounce(...)) with useMemo for debounced search handlers
• Avoid mutating props, state objects, and i18n store data in place
• Replace delete on optional chaining with omit() or i18n.reloadResources()

Follow-up

Remaining warnings are tracked in #52900 (primarily useRoutableTab hook wrappers).