fix(ERP-241): use InvalidArgumentException in TimetableService for proper error display

fix(ERP-241): use InvalidArgumentException in TimetableService for proper error display

TimetableService threw generic \Exception which EventBehavior couldn't
handle, causing "Произошла неизвестная ошибка" in mobile app instead of
actual validation messages. Changed to InvalidArgumentException (matching
pattern used by all other api3 services) and switched from Json::encode
to firstErrors[0] for human-readable messages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>