Make the PASS notice name the HTTP API login (closes #217)

After PASS on the IRC listener, the confirming NOTICE told the user to
reconnect with PASS and their nick. The IRC listener cannot add a
connection to an existing session, so that step does not work. The
notice now says the password is set and that another client can log in
to the session over the HTTP API with POST /api/v1/login, as the README
describes. The test now checks the whole notice text.

Model: opus-5-5

internal/ircserver/commands.go

@@ -1227,9 +1227,12 @@ func (c *Conn) handlePassPostReg(
 		return
 	}
 
+	// The IRC listener cannot add a connection to an existing
+	// session; only the HTTP API login can.
 	c.sendFromServer("NOTICE", c.currentNick(),
-		"Password set. You can reconnect using "+
-			"PASS <password> with your nick.",
+		"Password set. Another client can log in to this "+
+			"session over the HTTP API: POST /api/v1/login "+
+			"with your nick and this password.",
 	)
 }