Avatar images failed to load with 403 on Tigris and newer AWS S3 buckets
because getAvatarUrl only constructed path-style URLs. Modern S3-compatible
providers require virtual-hosted URLs (bucket.domain/key).
Add NEXT_PUBLIC_STORAGE_DOMAIN env var to signal URL style:
- If set: virtual-hosted URL (Tigris, AWS S3)
- If not set: path-style URL (MinIO, LocalStack) - backward compatible
Add vitest and tests for getAvatarUrl behavior.
Co-authored-by: Sachin Divekar <sachin.divekar@remiges.tech>
