Wires @Valid on the @RequestBody parameter of TranscriptionBlockController's
createBlock and updateBlock methods so JSR-303 actually fires for incoming
DTOs. With @Valid on the field-level mentionedPersons in the DTO (added in
the previous commit), Jakarta validation now recurses into each
PersonMention element and rejects displayName values past the @Size(max=200)
ceiling.
The test posts a 201-char displayName and asserts the global handler maps
the resulting MethodArgumentNotValidException to 400 + code:VALIDATION_ERROR.
Refs #362
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
4e8df66a79