feature: chat attachments and GIPHY GIFs

[lukepolo]

Lets players attach up to four images or videos to lobby, tournament, organizer, draft and direct messages, and send GIPHY GIFs, with every file cleaned up automatically.

• Uploads go through the api in 8 MiB streamed parts, held to the admin settings for file size and daily allowance (chat_attachment_max_mb, chat_attachment_daily_mb), with the type and image size read from the bytes
• A send checks the files are the sender's, finished and for the same room; match and team rooms stay text-only and gagged players are refused
• Files are served only to people who can open their room, revalidated on every view with Range support for video; a deleted group message's files stay visible to staff until they expire
• Files are deleted at the room's TTL, with their direct message, after 24h if never sent, and by a daily version-aware sweep
• GIPHY search goes through the api with the admin-only key and an hourly panel-wide limit (giphy_hourly_limit), with no rating filter; messages carry only the GIF's id

From DEAFCS: DEAFCS/api-deafcs@f739e383 DEAFCS/api-deafcs@df516d49 DEAFCS/api-deafcs@82de188f DEAFCS/api-deafcs@7b5ca049 DEAFCS/api-deafcs@33032e1b