[feat. req.] exploding messages magic command

People should be able to send off differently timed exploding messages with the flick of the wrist, not multiple mouse clicks.

How about some kind of magic text?

`!90s hello world` would explode in 90 seconds
`!24h hello world` would explode in 24 hours
`!7d hello world` would explode in 7 days
`!1w hello world` would explode in 1 week
etc.

(I have no idea if this is feasble or not. A keyboard shortcut would also be great!)

The issue names no files, tests, or entry points. Start by locating the message composer and the existing exploding-message implementation, then determine where command parsing and expiration scheduling belong. Done should include the requested duration formats, a defined behavior for invalid input, and coverage for each supported unit.

Written by the indexing model from the issue text.