Replace five duplicated uuid::Uuid::parse_str calls in web handlers
(analyze, document view, delete, reset, case detail) with a
CaseIdPath extractor that validates the URL segment once and
returns the legacy "Invalid case_id" 400 body byte-for-byte.
The extractor uses axum's FromRequestParts and maps any failure
to AppError::BadRequest, so IntoResponse handling is unchanged.
Brummel