Discord introduced message_snapshots for forwarded messages — text and
attachments live inside snap.content / snap.attachments rather than on
the parent message. _handle_message wasn't reading them, so forwards
showed up empty.
Defensively extracts snapshot text (when raw_content is empty) and
appends snapshot attachments to the working all_attachments list used
for type detection and media routing. hasattr/getattr guards keep this
safe on older discord.py installs without the field.
Salvage of #25462 by @1RB (manually re-applied — original branch was
stale against current main).
b59ed9c6bc