uploadMedia() had no content-type check, so an HTML login-redirect response
from an auth-protected internal endpoint was uploaded to Bluesky as a blob
with encoding "text/html". uploadBlob() accepts it, but record validation
rejects the post with 'Expected "image/*" (got "text/html")'.
The patch mirrors the guard already present in uploadImageFromUrl() and also
wraps per-photo uploads in try/catch so one bad photo doesn't abort the
entire syndication — other photos and the post text are still published.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
