bingo: fix photo rebuild on UTF-8 tagged S3 bodies

aws-sdk returns object bodies from a plain StringIO, so S3.get handed
back a UTF-8 tagged string and Photo.sniff's binary prefix comparison
raised Encoding::CompatibilityError: "Rebuild resized photos" died on
the first photo with a 500. URL imports had the same flaw via a UTF-8
read buffer. Treat image data as binary at the source and in sniff, and
let one failing photo no longer abort the batch (errors are reported in
the admin flash and logged).

Assisted-by: Claude:opus-5

lib/bingo.rb

@@ -138,7 +138,10 @@ module Bingo
 
     module_function
 
+    # Input may arrive tagged UTF-8 (aws-sdk bodies are plain StringIOs), and
+    # comparing that with binary literals raises, so look at raw bytes.
     def sniff(bytes)
+      bytes = bytes.b
       return 'jpg'  if bytes.start_with?("\xFF\xD8\xFF".b)
       return 'png'  if bytes.start_with?("\x89PNG\r\n\x1A\n".b)
       return 'webp' if bytes[0, 4] == 'RIFF' && bytes[8, 4] == 'WEBP'
@@ -175,6 +178,7 @@ module Bingo
     end
 
     def build_variants(key, bytes)
+      bytes = bytes.b
       ext = sniff(bytes) or raise Error, 'not an image'
       WIDTHS.each { |w| S3.put(variant_key(key, w), resize(bytes, ext, w), content_type: TYPES['webp']) }
       true
@@ -198,6 +202,8 @@ module Bingo
       out.b
     rescue Errno::ENOENT
       raise Error, 'ImageMagick (convert) not installed'
+    rescue Errno::EPIPE, IOError => e # convert exited before reading all input
+      raise Error, "convert: #{e.class}"
     end
 
     # Photos are served byte-for-byte, so drop EXIF/XMP/IPTC/text metadata:
@@ -276,7 +282,7 @@ module Bingo
             raise Error, 'too many redirects' if redirects.zero?
             return fetch(URI.join(uri, res['location']).to_s, redirects: redirects - 1)
           when Net::HTTPSuccess
-            body = +''
+            body = +''.b
             res.read_body do |chunk|
               body << chunk
               raise Error, 'image too large (max 8 MB)' if body.bytesize > MAX_BYTES