All 30+ journey_* message keys added to de/en/es.json. Four new ErrorCode
values for journey item operations wired into errors.ts + getErrorMessage().
Interlude CSS primitives (--c-interlude-bg/border/label) defined for light
and dark themes so JourneyItemRow can reference them via semantic aliases.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>