fix(infra): make the recovery hostname unique per provisioning run

The preflight hostname listing is check-then-create, so two concurrent runs
with the same LATITUDE_HOSTNAME could both pass it and create two billed
servers behind one recovery correlation value, which hostname recovery then
refuses to disambiguate. Latitude enforces neither hostname uniqueness nor
create idempotency, so uniqueness is generated locally: every run appends a
random 8-hex suffix to the (now max 23 char) base hostname, keeping the
correlation value unique across concurrent runs. The preflight check stays
as defense-in-depth against pre-existing duplicates.

Co-authored-by: Cursor <cursoragent@cursor.com>