A failed login keeps its username in the in-memory log buffer, the
limiter table and the notifier queue, and the route accepted any body
the global cap allowed. The login route now takes at most 16 KiB and
answers a username over 256 bytes with the generic failure before any
of those see it; the user setters refuse such a name too, so no stored
username can be one the login route turns away.
The first user is now created when the server starts, with a random
username and password printed once to its log (docker logs, the journal),
instead of a fixed pair seeded by InitDB. CLI calls that initialize the
database are often piped away, as the Docker entrypoint's port lookup is, so
only the server's own log reliably reaches the operator.
`x-ui setting -show` keeps reporting hasDefaultCredential: true until a user
exists, so install.sh still sets its own credentials on a fresh install.
Existing databases are not changed. Verified on a built binary: fresh
setting -show, install.sh-style credential set, first start, login and
restart. The PostgreSQL lane was not run locally; the change adds no query.
MHSanaei