pub fn generate_invite_code() -> Result<String>Expand description
Generate a random, unguessable invite code of the form FEATHER-XXXXXXXX.
Draws from the OS CSPRNG (getrandom) and maps each byte onto
[CODE_ALPHABET] via rejection sampling so the alphabet distribution is
uniform (no modulo bias). Infallible in practice; a getrandom failure
(no entropy source) propagates as an error rather than a weak code.