fix(errors): SSH tunnel failures are reported as a database authentication failure #1305

Problem

SshAuthenticationException text is SSH authentication failed for user@host: .... mapDatabaseError (lib/core/database/database_error_mapper.dart) matches authentication failed and returns AuthFailedException with Check the username and password in the connection settings, and describeDatabaseError returns only displayText.

The user sees Authentication failed. Check the username and password in the connection settings for a wrong bastion password or key. The bastion host, the user and the reason are lost, and the hint sends them to the database credentials.

Related: a network failure before authentication (client.authenticated throws a socket error) is also wrapped as SSH authentication failed ... $e (ssh_tunnel_manager.dart, after await client.authenticated).

Scope

• Handle SshAuthenticationException / SshHostKeyMismatchException before the generic text matching: a mapped SshTunnelException (or keep their text) with the host, user and cause, and a hint about the tunnel settings.
• Tell a transport failure (timeout, refused, reset) from a rejected login in openTunnel.

Acceptance

• A wrong bastion password shows the bastion host and an SSH-specific message, not the database hint.
• A bastion that does not answer is reported as unreachable, not as an authentication failure.
• A database password authentication failed behind a working tunnel is still reported as a database authentication failure.