fix: align endpoint_mismatch diagnostic code with check id and span raw endpoint string

- Change EndpointMismatchError diagnostic code from labeler_endpoint_matches_flag to resolved_did_matches_flag
- Fix span lookup to use raw endpoint string from DID doc service entry, not normalized Url
- Query find_service to get raw service_endpoint and span that instead of normalized Url
- Regenerate endpoint_mismatch snapshot showing correct diagnostic code and span

Fixes I-NEW-4: Diagnostic code now matches check id, span points at actual endpoint string in JSON

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>