List the missing channel modes in the 004 reply (closes #238)

The channel-modes parameter of RPL_MYINFO left out modes that each
transport's MODE accepts. The IRC listener now sends Himnostv, adding
H, i, o and v. The HTTP API now sends Hbiklmnostv, adding H, b and v.
Each transport keeps its own list, because they accept different
modes. The tests compare the whole parameter, so a missing or extra
mode fails them. The README and the schema notes show the new HTTP API
list.

Model: opus-5-5

internal/handlers/api.go

@@ -412,7 +412,7 @@ func (hdlr *Handlers) deliverWelcome(
 	// 004 RPL_MYINFO
 	hdlr.enqueueNumeric(
 		ctx, clientID, irc.RplMyInfo, nick,
-		[]string{srvName, version, service.UserModes, "ikmnostl"},
+		[]string{srvName, version, service.UserModes, "Hbiklmnostv"},
 		"",
 	)