Distinguish CORS failures from generic network errors #1163

Background

CORS rejections are reported identically to generic network errors, hiding backend/misconfiguration issues. Detect and tag them separately.

Files to modify (2-3)

src/lib/apiInterceptors.ts
src/services/errorReporting.ts

Acceptance Criteria

Implemented across the listed files

Unit/integration tests added or updated and passing

No regression; follows project coding standards