47b1ad6199
New 400 error code for a relationship whose toDate precedes its fromDate,
registered in all four sites at once (ErrorCode.java, errors.ts,
getErrorMessage, messages/{de,en,es}.json) per constitution §3.6. Thrown by
the relationship date validation introduced in the following commit.
Refs #837
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>