Fix IRC listener relay of bodies and modes, and JOIN names (closes #127)

The IRC listener relayed only the first line of a PRIVMSG or NOTICE
body; it now sends one line per body line. A MODE change reached IRC
listener members without its key, limit or mask, and "+o bob" went out
as one trailing parameter; each value is now its own parameter, in the
relay and in the echo to the IRC listener user who made the change. The
channel name check moved from the HTTP handler into
service.JoinChannel, so the IRC listener's JOIN refuses the same names
with 403.

Model: opus-5-5

internal/ircserver/commands.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"slices"
 	"strconv"
 	"strings"
 	"time"
@@ -683,9 +684,11 @@ func (c *Conn) applyChannelModes(
 	if applied.Len() > 0 {
 		modeReply := applied.String() + appliedArgs.String()
 
-		c.send(FormatMessage(
-			c.hostmask(), "MODE", channel, modeReply,
-		))
+		params := slices.Concat(
+			[]string{channel}, strings.Fields(modeReply),
+		)
+
+		c.send(FormatMessage(c.hostmask(), "MODE", params...))
 
 		c.svc.BroadcastMode(
 			ctx, c.nick, channel, chID, modeReply,