Images now load direct from images.04080616.xyz. Removes read-side
signing (signUrl/signCoverUrls + callers), unlocking browser and
edge caching since URLs are stable. Presigned upload kept for /api/upload.
PageReader retries failed loads via onError as a safety net.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>